OEM MK4 management wiring => Mk1/2/3 harness install FAQ (Now with added dieselness!)

How do all! Finally decided to write a new OEM guide containing everything I have learnt over the last couple of years making looms and trawling diagrams! Many thanks to 20v_Jimmy who created the original 20v OEM guide thread here:
http://www.clubgti.com/showthread.php?205887

Just an important note to start with don't go by wire colours in this guide, rather check the pin locations. Not all MK4/SEAT/Audi looms use the same wire colours but 99% of the time the pin locations are the same. The colours in this guide are based on an AUM/AUQ loom, AGU for example can differ here and there. If in doubt check the various wiring diagrams in the link in my signature Also if you have a diesel engine make sure you read all the diesel notes carefully as there are a few pins which differ vs the petrol looms.

My aim with this thread is to cover as many MK4 conversions as possible rather than AUM/AUQ specifically, and also cover the splicing of them into both CE1 and CE2 fuseboxes. The process for all the MK4 looms I have seen so far is basically the same, just a few tweaks required depending on the age and type. You have 2 main types of loom in a MK4, DBW and non DBW or I suppose you could break it down to those with an ECU relay and those without really. The DBW pedal makes no real difference on its own as that is wired straight to the ECU anyway, so requires no thought apart from how to fit it to the car.
Also for the section with the coloured plugs you have early and late type, though the early ones were only made for a year or so. The early looms have a couple wires switched over but apart from that they are the same as the later type, they have a green plug rather than white so easy to identify.

Now to get started. All you really need from the donor MK4 are both halves of the ECU loom, then to make the loom my way you will also need a 10 or 14 pin plug cut out of a donor MK4 so the 2nd half of the ECU loom can simply plug in. Early MK4 looms use a 10 pin plug, later looms use a 14 pin. They carry the same signals however the pinout is slightly different but I will cover this later. From now on I shall refer to this plug as T10a or T14a as this is how it is labelled in the VW wiring diagrams. You could just splice the T10/14a wires direct to your engine loom if you prefer

In early cars the T10a plug is located in the plastic loom channel on the passenger side chassis leg. It is also used on the headlight looms on both sides of the MK4 as well as many other VAG motors. The T14a plug is found tucked next to the battery clipped to the chassis, its pretty well buried! Cut out as much length on the wires as you can, it will make it easier to fit later.

Ok now you will need to either remove the engine loom from your own car, or find another engine loom with the same fusebox plugs on to use as your base. If you have a MK1 Golf you can use any engine loom you like really there's no difference once you strip out the bits you don't need. In fact if you start with a carb loom it actually makes your life a little easier as it has an extra pin you will need later which the kjet GTI looms don't have! If you have a MK2 Golf the above applies, except if you want the MFA to work start with a GTI loom of some kind as the wiring for this is part of the engine loom. If you have a CE1 MK2 Golf try to get a digifant engine loom, this is the easiest base to start from. For MK3 Golf apart from the MFA wiring you can start from any MK3 loom, but note is there are 2 types of loom on the MK3! You have the early type where the engine and lighting looms are separate and the later looms where its all bundled together. Ideally you want to get the same type as fitted to your car, otherwise you'll have a lot of faffing ahead of you.

First of all strip your old loom of all of its insulation/tape, you'll want to keep all the wires to the fusebox but you can chop off all the engine specific plugs at the other end. Keep all the oil and coolant wires as well as the wiper wiring. If you have terminal removal tools it can be useful to pop pins out of the housings rather than snip the wires, plus make a judgement call on the condition of your wiring if its all grotty you may have to chop it back a bit further till you get to nice fresh copper. If its a GTI or MK3 there is an extra earth wire from the dash which you'll need to keep. CE1 cars this is a brown/white wire with a female spade, for CE2 cars this is a brown/white wire in G1/5. Either way this wire is earthed to the side of the head, but for neatness you can earth it inside the car if you like. On a related note CE1 cars with MFA will have connections for the outside temp and oil temp sensor separate to the fusebox which you'll want to keep. Early CE1 MK1 GTI have the MFA oil temp to the fusebox and have the yellow 0.24/0.3bar oil switch wire to a spade near the fusebox instead. Once you've trimmed it all back you should be left with something like this:


Next fully strip the large plug MK4 ECU loom of its tape. The carbon canister can go but keep the blue/yellow wire to it for now this is a fuel pump power feed and may come in handy later, just chop out the purple/red wire back to the ecu. If you plan to map out the post-cat lambda(s) you can remove the wiring now, or leave it and get shot of it later on. The PAS pressure switch can go as can all the SAI pump, relay & valve wiring if fitted. Also you can remove the starter and reverse switch wires, you may want to put this to 1 side for later depending on the condition of these wires in your old loom. plus you may need the plug ends if you keep the mk4 starter/reverse switch. Note the large brown/red wire with ring terminal, this is the main ECU earth. I extend it to reach the battery, but as long as you have a good clean earth point anywhere will do.

Next if you have a loom with an ECU relay make a choice now, you can either leave the MK4 relay box in place or chop it out and fit the ECU relay above the fusebox. If you decide to move the relay pull the purple wire from it back to the fusebox end of your ECU wiring, we will need this later. Also keep the large 2 pin plug with the single white/red wire, this is needed to power the ecu and coils (plugs into the small ecu plug loom) finally carefully cut off the rubber plate/plastic cover on the coloured plug end. there is a thick chunk of plastic sealed with glue over the wires, carefully cut a slit in it then split it open. Then the glue should chip off easily. Should end up with something like this (note PAS switch not chopped off yet)


Ok getting there! When I make my looms for MK2 Golf I mount the ECU in the middle of the scuttle just under the wiper motor using the middle hole in the scuttle near the coil, I also pull the wiper loom back across and put it thru that hole as well chopping it down to suit. This leaves the old wiper grommet hole spare for the small ecu plug. On a MK3 loom I run the large ecu plug in with the wiper loom on the driver side, leaving the ecu grommet on the passenger spare for the other loom. On the MK1 again I use the wiper loom hole into the scuttle, though you may want to make the hole larger if its an older car. Top tip from Hilux in another thread for this job:


Next its time to join your 2 looms together. Lay them both in your engine bay where you want them and tape together. MK1 owners rejoice as the MK4 loom should reach the fusebox no problem, but MK2 and MK3 owners will have a fair bit of extending to do. Next lay the other half of the MK4 ECU loom into position and tape your T10/14a plug where it needs to be, along with the 2 pin plug if you have an ECU relay.

Take it all out and lay it down on your bench, now for the fiddly wire joiny stage! Here's a chart showing the pins, I have tried to cover all types of MK4 loom plus MK1/2/3 as well so hopefully it makes sense lol Don't worry too much about the wire colours in the chart these can differ depending on the age/donor, rather concentrate on the pin functions.

For more information on the CE1/CE2 fusebox side of things, be sure to check my Fusebox FAQ

T6 - brown 6 pin connector, early:

Pin #	Colour	CE1	CE2	Notes
1	blk/pur or blk	Ignition live or ECU relay power, see notes below!
2	red/brn	bin		Use original wires for reverse switch
3	red/blk	bin		Use original wires for starter motor, or if you can de-pin it nice and you're converting a CE2 MK2 Golf this wire will actually fit the mk2 fusebox and reach. Handy if using a mk3/4 golf starter it'll then plug in no need to splice the end to the old wire. MK3 Golf starter motor wire already fits the MK4 starter so no worries. For CE1 cars you'll need to change the starter end to suit, a 'standard timer' pin is used in the mk3/4 plug if you can depin or splice. can be tricky though due to wire gauge.
4	red/grn or blu/yel	Fusebox spade P or ECU relay power fuse (petrol) ECU relay power (diesel)	G2/9 (DBC, some DBW) or Y spade or ECU relay power fuse (petrol) ECU relay power (diesel)	Permanent live to ECU on petrol models. Also used for ECU+coilpack relay power on some DBW models, for these you need a decent 12v feed from battery or Y/P spade. So for example G2/9 isnt going to cut it. Is fed by ECU relay power on diesel models. see diesel & ECU relay notes below for more information
5	blu/yel	E/14 via male spade or N with fuse (petrol) ECU relay pin 87 (diesel)	G1/8 (petrol) or Z/1 with fuse (petrol) G1/10 or ECU relay pin 87 (diesel)	Fuel pump live for lambda heater, MAF, carbon canister etc on petrol cars. ECU relay power on diesel models (see diesel notes below) make a judgement call where to take the feed from, based on how much load will be on this feed. DBC have pretty much nothing on this, DBW have a fair bit more load but then you may decide to delete most of it.
6	yel/blk	E/14 via male spade (petrol) or N with fuse ECU relay pin 87 (diesel)	G1/8 or Z/1 with fuse (petrol) G1/10 or ECU relay pin 87 (diesel)	As per T6/5 fuel relay power on petrol engines, ECU relay power on diesel models. Only in use on some engines, often either low load or for things that can be deleted. As above make a judgement based on what is fed from this pin to decide how to power it if at all. For example some dieselhave this to auxiliary heater relay trigger and/or breather heater, could be run to an ignition live rather than ECU relay as its not under any load. On R32 looms this only feeds SAI and carbon canister, both of which can be deleted on convertion looms.

T6 - brown 6 pin connector, late as per early plug except:

2

pur/wht

D/13

G1/3

Fuel pump relay earth trigger for petrol models. Glowplug relay for diesel models (see diesel notes below)

T10 - orange 10 pin connector, early:

1	gry/wht	to vag-com port pin 7		Diagnostics K line
2	grn/wht	bin	bin, or clocks on MK3	MPG signal, bin on MK2. On MK3 and some other later VAG such as Corrado/Passat etc this goes to the purple/white wire on the clock plug. I've heard reports the signal is compatible
3	pur/wht	D/13	G1/3	Fuel pump relay earth trigger for petrol models. Glowplug relay for diesel models (see diesel notes below)
4	wht	bin		Feed to radiator fan control unit (climatronic?)
6	blu/wht	yel/wht from radio/dash plug	W/1	Speed signal output from dash, need to have a GTI cluster or speed sender fitted to back of clocks before this will work in MK1/2. In Corrado, Passat & MK3 these usually have a blue/white wire jumper block above fusebox you can use (see notes below)
7	grn	bin		Aircon 'compressor switch off'
8	blu/red	bin		Aircon 'aircon ready'
9	grn/brn	D/26	G1/12	Rev counter, need tach adaptor for MK1/2 & early Corrado cluster. Later Corrado and MK3 can use this signal directly (see notes)
10	blk/blu	bin		Use original wires for reverse switch

T10 - orange 10 pin connector, late as per early plug except:

3

red/brn

bin

Use original wires for reverse switch

T10w - white or T10d - green 10 pin connector

		CE1	CE2
1	wht/red	bin?		to vag-com port on AGU ecu. I have information that you put 12v to this wire then switch on ignition and leave it on for a while when you want to flash the ECU (see page 2) but that's all the information I have currently!
2	org/blk	to vag-com port		CAN-BUS generally not needed, if you ever plan to sniff CAN packets then you can run these to the fusebox area just in case
3	org/brn	to vag-com port		CAN-BUS generally not needed, if you ever plan to sniff CAN packets then you can run these to the fusebox area just in case
4	wht/red	to clutch pedal switch		For DBW ECU you will get rev hang between gear changes without this, DBC don't seem to mind. Also needed if you want launch control. Either way I would recommend you at least run the wire so you can add the switch later if need be.
5	blu/pur	alternator pin DFM		Only used on some models, see notes below
6	brn/wht	bin		connection for radiator fan control unit, generally unused.
7	wht/grn or pur/yel	D/13 or fuel relay pin 85	G1/3 or fuel relay pin 85	unused on petrol engines, on some diesel engines this is used for an electric pre-supply pump (see diesel notes below)
8	wht/red or blu/grn	bin		EPC fault lamp
9	grn/pur	bin		Crash signal
10	pur/yel	bin		Emissions fault lamp

T10e - black 10 pin connector

1	blu/gry	bin	cruise control switch
2	red/yel	bin	cruise control switch
3	blk/wht	bin	cruise control switch
4	blk/red	brake light switch	Same as clutch switch seems you can have issues without, either way run the wires just in case
5	wht/yel	cruise control brake switch	Same as clutch switch seems you can have issues without, either way run the wires just in case
9	wht	bin	cruise control switch

T10h - blue 10 pin connector

1	brn/wht			accelerator position sender pin 6
2	grn/wht			accelerator position sender pin 1
3	brn/wht			accelerator position sender pin 2
4	gry/red			accelerator position sender pin 3
5	wht/blu			accelerator position sender pin 4
6	gry/blul			accelerator position sender pin 5
7	yel/brn	bin		Fuel system diagnostic pump
8	blu/yel	ECU relay pin 85	ECU relay pin 85 or G1/7	ECU relay on diesel models (see ecu relay and diesel notes below)
9	grn/pur	bin		Fuel system diagnostic pump
10	blu/pur	bin		Automatic gearbox control unit pin 56 (speedometer signal)

T10a - 10 pin connector in engine bay near ECU:

1	blk	D/1 or D/21	G2/10 or G2/11	Oil pressure switch, see notes below
2	blk/wht	bin or D/2, D/7 or G spade 3 or 5	bin or G1/4 or G2/4	Ignition live feed for speed sender, unused unless you have electronic speedometer
3	n/a
4	pur	D/29	G2/3	Coolant sender for dash, see notes below
5	red/pur	Large spade N ECU relay pin 87 (diesel)	Z/1 ECU relay pin 87 (diesel)	Fuel pump live for injectors, diesel pump on non-PD engines
6	yel/blk	E/14 via male spade or N with fuse (petrol) ECU relay pin 87 (diesel)	G1/8 or Z/1 with fuse (petrol) ECU relay pin 87 (diesel)	Fuel pump live for valves/actuators on main ECU sensor harness. ECU relay power on diesel models (see diesel notes below)
7	brn	earth to battery		Coilpack earth
8	blk/pur	ECU Relay pin 87 (some petrol)	ECU Relay pin 87 (some petrol)	Coilpack power feed on some 4 cylinder engines, or unused
8	blk/pur	Large spade N	Z/1	Fuel pump live for injectors (some 5/6 cylinder engines, can also use ignition live for this if easier)
9	brn/wht	earth to battery or head		Earth for dash temp sender
10	wht/blu	bin or direct to clocks	G1/11	Signal from speed sender, unused unless you have electronic speedometer

T14a - 14 pin connector, as per T10a except:

3	wht/blu	bin or direct to clocks	G1/11	Signal from speed sender, unused unless you have electronic speedometer
10	grn/gry	bin		Aircon thermoswitch F163, new beetle
10	blk/grn	G spade 1 or 3	D/3, D/5 or D/7	X-over live, so only live with ignition NOT cranking, only on some diesels
11	yel/blk	bin		Oil level/temp sensor ignition live feed
12	pur/wht	bin		Oil level/temp sensor to dash (only works MK4 cluster)
13	red/blk	To fan control unit or fan after-run relay		Power feed for electric coolant pump, only on 5/6 cylinder engines.
14	gry/blu	bin		R32 exhaust flapper valve
14	grn/brn	bin		Aircon thermoswitch F163, new beetle

T2 - 2 pin connector in engine bay near ECU: (Only on looms with an ECU relay, or diesels)

1	blk/pur	ECU relay pin 87 or MK4 relay box plug (petrol) or Glowplugs	Coilpack & ECU power feed, either use your own relay or the factory MK4 relay (petrol, see ECU relay notes) or Glowplug relay (see diesel notes)
2	blk	Glowplugs	Glowplug relay (see diesel notes)

MK4 Diesel engine notes:
For the diesel engines the wiring is mostly the same with the exception of the glow plug and on later models the pre-supply pump. If you have an early one without a supply pump use a 67/80/167 fuel pump or MK1/2/3 glow plug relay in your fuel pump socket, and run your glow plug power with suitable inline fuse to large spade N for CE1, or Z/1 for CE2. This will make it as per OEM MK1/2/3 diesels. If you have a later one with a pre-supply pump, you can either add your fuel relay above the fusebox triggered from T10w/7 like how it is on a MK4, or my personal preference is use the fuel pump relay socket for this then that way you can use a factory mk1/2/3 GTI rear wiring loom to power the pump and instead fit the glowplug relay above the fusebox. The diesel engined cars have the ECU relay inside the car, I would put it above the fusebox as per the notes below. Also note T6/4 differs on the diesel lumps, on the petrol engines its permanent live but in the diesel it expects a ECU relay power feed. So feed this with the output from your external ECU relay along with all of the other ECU relay power feeds.

Either way wire the external relay like this:
30 - permanent live (spade P CE1, or Y CE2)
85 - fuel trigger T10w/7 or glowplug trigger T6/2 or T10/3
86 - ignition live (D/2 or D/7, or G spade 2 or 5 CE1, G1/4 or G2/4 or D/8, 9 or 11 CE2)
87 - power to glow plugs or fuel pump

The glowplugs require a 50a fuse if you feed all 4 from the same fuse, various factory glowplug fuses are available you can re-use or you can use a maxi type fuse holder. anoher option is to install a mk4 golf battery fusebox and use a 50a from that to feed your glowplug relay power input. Alternatively, since the glowplugs split into 2 feeds you could run the output from your relay to them via 2 fuses if its easier for you.

Fuel pump relay notes:
Usually a 67/80 or 167 relay will work just fine, but Andy947 has found that on his BDE ECU it sent a pulsed signal rather than an earth trigger so he had to use a MK4 409 fuel pump relay so bear this in mind when trying to fire your motor up for the first time.

Rev counter:
The MK4 ECU outputs a low amp signal which wont work with MK1/2 type clusters, for these you will need some kind of adaptor. You can find adaptors from several sources online, most of the wiring specialists can sort you one. This signal is compatible with MK3 and late Corrado however, so no problems there. The other thing to note is if the engine has 5 or 6 cylinders then you will also need an adaptor capable of converting this signal to 4 cylinder pulse, or in the case of MK3/Corrado you can use a set of VR6 clocks instead. This unit has been proven to work converting 6 cylinder MK4 signal to suit MK2 clocks:
http://ashlocktech.com/Home.php

Oil temperature and/or pressure switch(es) notes:
You can splice one of your old oil pressure switch wires to the T10a/14a plug if you like and make use of the MK4 wire, you could make use of the unused pins and run all of them through the T10a/T14a. These days I re-use the oil level/temp wire feed for oil temp as technically its the same thing, use the old MK4 pressure switch wire and use one of the spare holes for the 2nd pressure switch. Or you could just run the original wires to the switches direct and bin the MK4 pressure switch wire. If you use the MK4 wire unless its really early the plug will want chopping off and a spade crimping on. The MK4 pressure switch is no good so bin it, also you will note that (usually) there is a spare oil tapping in the filter housing, remove that as well. Then fit the blue or brown switch 0.25-0.3bar switch part number 028919081, 028919081B or 028919081H in the spare hole, and the white 1.8bar switch part number 056919081E or 056919081 where the MK4 switch used to be. If you have an MFA cluster you will also need to get an M10x1 thread T piece and fit the old oil temp sender into one of the holes here as well. You should end up with this:


Coolant temp sensor notes:
The MK4 4 pin coolant temp sensor will not work correctly with a MK1/2/3 dash temp gauge, there are a few ways round this:
1. Fit a 39ohm resistor (33ohm previously suggested, but have reports that 39 works better) inline with the T10a/14a plug pin 4. I've heard mixed results from this, some say all is well but when I tried it the gauge didn't work at all till it was removed.

2. Fit a MK3 golf 1.8-2.0 8v 4 pin coolant temp sensor part number 357919501A or 6U0919501B, splicing the matching plug part number 357919754 to suit if necessary. This is my personal choice as it works fine with the MK4 ECU and MK1/2/3 clocks no resistors are required! If you need to splice the early plug onto a late loom the pin numbers differ.

MK3 sensor pins:
1 - brown/blue - ECU sensor earth
2 - brown - dash sensor earth
3 - blue - ECU sensor signal
4 - yellow/red or blue/white - dash sensor feed

Late MK4 sensor pins:
1 - purple - dash sensor signal -> MK3 plug pin 4
2 - brown/white - dash sensor earth -> MK3 plug pin 2
3 - grey/yellow or blue - ECU sensor signal -> MK3 plug pin 3
4 - brown/blue - ECU sensor earth -> MK3 plug pin 1

3. Fit a MK4 upper rad hose with sensor fitting part number 1J0121087A and add a MK2 golf 2 pin black coolant temp sensor, splice MK1/2/3 dash sensor signal to one of the pins and earth the other pin:


VSS notes:
For CE2 fusebox this is easy, pop a wire to W/1 and usually you are done. For GTI MK2, all MK3 and corrado this pin is always active. For poverty spec MK2 you will need to either change the clocks for GTI ones, or you can add the speed sensor to the back of the clocks. You might need to change the clock wiring as well, the MFA stalk wires are not fitted on non-GTI but I'm not 100% sure on the VSS signal wire. It runs from U2/2 on the fusebox to pin 7 on the clocks anyway.

CE1 this isn't always so easy. For late MK2 Golf, Cabrio and Scirocco you will sometimes find a yellow/white wire from the clocks to the radio and/or a spade connector in the fusebox area, if present this is your VSS feed. As above unless its got GTI clocks there is no speed sensor on the clocks so swap GTI clocks in or depending on age/type of clocks you can sometimes add the speed sensor to the back. If the wire is not there then you need to find a donor dash harness to pinch a pin from, note MK1 Golf, Cabrio & early Scirocco clock pins are not the same as MK2 Golf & late Scirocco so make sure its the right type to match your cluster harness. For the MK1 type clock plug the pins in the handbrake/choke warning light plug are the same. Sometimes you can find a spare wire in here left over once conversion is done, but don't touch the black and green/white wires as those are for handbrake light.

For VSS pin numbers see the CE1 section of the Fusebox FAQ

ECU relay notes:
Regarding brown plug T6/1 this is a little complicated so bear with me! To start with if you have a DBC loom which doesn't have an ECU relay in the engine bay then run this to your ECU relay power pin 87, simples. Put a 15a fuse on this pin or pin 30 power input to the fuse as failed coilpack or shorted harness can melt this wire pretty quick otherwise.

If you have a later DBW loom with an ECU relay in the engine bay then you will only need to run this pin to an ignition live source, no need for a relay. So D/2, D/7 or G spade 2 or 5 for CE1, and for CE2 G1/4 or G2/4, or D/8, 9 or 11. For CE2 I'd go with G2/4 if you have the choice as its fused and keeps it all part of the engine harness, all the CE1 listed pins are fused. On DBW looms this pin is used as an ignition sense, then the ECU will trigger its own ECU relay for main power and coilpack power. Weird I know!

With the DBW looms you have 2 choices with the main ECU/coil power relay, either leave the factory relay box in place and mount it to the scuttle or move the relay to the fusebox area. I wouldn't recommend you use the factory socket on a CE2 fusebox, it is unlikely to be able to take the load. If you move the relay the old purple trigger wire from the ECU will need to go to the ECU relay pin 85. When mounted above the fusebox you could use a 109 relay or a standard switched live relay see the notes below. You can of course just ignore the purple wire and wire it as per standard AGU looms if you do that the ECU will flag a code.

When mounting your ECU relay & fuses above the fusebox you can get nice relay holders from many VW/SEAT in the scrappy if you don't have any to hand or buy new ones from VW. I would recommend you pop a 15a fuse inline with the power input to pin 30 or power output on pin 87 as the DBW looms are prone to cracking up on the coilpack wiring, plus a failed coilpack can put excessive load on the power feed. You may as well pop the ECU permanent live from T6/4 in with the relay perm live input to pin 30, put it after the fuse so its fused as well.

If you keep the MK4 relay box then T6/4 powers both the ECU relay pin 30 and the ECU live feed, so you can give T6/4 a permanent live fused feed and that's 2 birds with one stone situation both coilpack and ecu live feed are fused same as factory MK4. If you have some standard timer pins you can make use of the empty fuse holders in the MK4 relay box for a nice OEM solution

DBC/Non-earth switched ECU relay type:
30 - permanent live (spade P CE1, or Y CE2)
85 - earth
86 - ignition live (D/2 or D/7, or G spade 2 or 5 CE1, G1/4 or G2/4 or D/8, 9 or 11 CE2)
87 - power for ECU/Coilpacks

DBW type earth switched relay loom:
30 - permanent live (spade P CE1, or Y CE2)
85 - purple earth trigger wire from ECU
86 - permanent live same as terminal 30 (VW 109 relay doesn't have this pin)
87 - power for ECU/Coilpacks

MK4 Diagnostics port wiring:
1 - black/blue - ignition live
4 - brown - earth
5 - brown - earth
6 - orange/black - CAN BUS high
7 - grey/white - Diagnostics K line
14 - orange/brown - CAN BUS low
16 - red/white - permanent live

Note all you need for basic diagnostics with VAG-COM/VCDS is live, earth and K line wires to pins 16, 4 and 7 though.

Clutch & Brake switches:
For DBW ECU without the clutch switch wired the revs will often hang between gear changes, but see how you go. Apparently the brake switch is needed for it to be 100%. For the DBC ECU you can ignore these wires they dont seem to care, but regardless I would still run the wires out to the fusebox then if you have any issues you can easilly wire them in. To bypass brake switch you need ignition live on the white/yellow and earth the black/red, this will fool ecu into thinking clutch isnt pressed and you'll find all the cruise brake binary bits set properly.

Clutch switch:
blue/black - ignition live
red/white - ECU pin 39 (petrol) 66 (diesel)

MK4 Brake switch pins:
1 - red/brown - original brake switch red/yellow (permanent live)
2 - blue/black - ignition live
3 - yellow/white - ECU pin 55 (petrol) 65 (diesel) (cruise brake switch)
4 - black/red - ECU pin 56 (petrol) 32 (diesel) & original brake switch red/black (brake lights on)

The MK4 Golf brake switch fits directly but be sure to hunt out a fitting guide as they can break if you dont follow the procedure. The MK4 clutch switch wont fit straight in but its easy to sort just file out some 'ears' into the original clutch switch hole so its the same shape as the brake switch. Alternatively MK2 clutch switch will fit straight in just ignore the vacuum connection, or SEAT Ibiza 99-01 fits in and doesn't have vacuum connection. With the brake switch you could also keep the original mk2 switch and add a 2nd cruise brake switch, the pedal boxes have 2 holes for this purpose.

Alternator DFM pin:
you can live without the DFM wire afaik, but I always put it in for my customers as I also run the blue alternator charge wire with the right plug to match the MK4 alternator cabling to make life as easy as possible. To do this on a MK1 or MK2 I move the alternator blue wire from the headlight loom to the engine loom, MK3 Golf, Corrado and a few others already have the alternator wire in the engine loom so sorted already. For the alternator blue wire on CE2 its pin F/3, CE1 its D/4.
Once that's done you can run your ECU DFM wire in with it to a 2 or 4 pin mating plug to match the alternator harness (2 pin for cars without A/C, 4 pin for cars with A/C) then it all plugs straight in.

Notes about fuses:
The MK4 has a much bigger selection of fuses than the CE1 and CE2 fusebox, so you'll note that pretty much everything has a fuse but when you compare to EFI looms in MK1/2/3 the same circuits are often not fused. The main ones we are concerned about are the fuel injector feed, permanent live feed to ecu, plus the ecu and coilpack power and lambda heater plus other accessory fuel pump power feeds. On a CE1/2 fusebox the fuel injectors, coil live, ECU switched power feed and perm live are not fused. I would say normally wiring the MK4 feeds the same way will be fine, however! As I keep saying I would definitely add a 15a fuse to your coilpack power, since some 20v looms suffer from the wiring cracking up and a failed coilpack can cause excessive load on the wire. If you're adding an ECU relay or re-using the factory relay box you may as well add a fuse while you're there anyway.

On the subject of cracked coilpack wiring, SEAT sell repair looms for DBW 20v so while you're making your conversion harness give the wiring a good check over and if any cracks are found bin it all and replace. Part number is 1J0971658L for 4 cylinder 4 pin coilpack cars without the oil level/temp sender sender, and 1J0971658M for those with oil/level temp sender. Only difference is level sender wiring, so you could go for non if you don't plan to use it anyway but the one with oil level/temp sensor wiring in is often cheaper! You can just chop out the level warning and speed sensor wiring if you dont need it. There are no repair looms for early 3 pin coilpack cars or for 5/6 cylinder that I can find but a later loom could be adapted if you have the required terminals and pin removal/crimp tools.

For the rest its up to you. VW have nice relay holders on various models that clip to the fusebox so I would source some of those if you want them, these use 'standard timer' type terminals which can be had quite easily new, or salvaged from old looms. CE1 P spades and CE2 Y spades plus G2/9 are not fused, neither is the large spade N or Z/1 for the fuel injector power, G1/10 on CE2 for ecu relay is not fused, but E/14 and G1/8 are both fused.

I would recommend any wiring which are exposed to potential heat and mechanical damage should be fused, the main ones being lambda wiring which runs underneath near the exhaust and the N75 valve which is close to hot turbo. Injectors are not so exposed and not so critical, as I say MK1/2/3 injector power is never fused. DBW wiring looms usually have a relay box attached for the coilpack and SAI, ythese have 3 or more spare fuse holders which are very handy as I mentioned in my notes about the ECU relay so you can make use of these for extra circuit protection. Or use OEM VW fuse holders which clip to the fusebox, part numbers below

Useful fuse and relay holder part numbers:
161937501/1H0937530 - fuse holder
161937501b - relay holder for 6.3mm spades (i.e. most switched relays)
867937501 - relay holder for 9.53mm spades (i.e. fuel pump and glow plug relays)
357937501 - double relay holder for 6.3mm spades

Feel free to ask questions and I'll update the thread if need be with the answers/corrections

 

2 errors there but they shouldnt affect the running, rev counter is T10 orange pin 9 not pin 2 and T14a/6 should be a fuel pump live not ignition live (just splice it into T14a/5 wire)

did you remember to run an ecu relay live to the 2 pin plug on the 2nd loom, purple/black wire? on the MK4 loom it would come from the relay box, if you left that as is you should be ok but make sure your coils get ign live if not the ecu may not be switching it. if you binned off the relay box then wire it up as per my info above with purple wire to G1/7 and 109 ecu relay.

with the fuel pump trigger it could be like a mk3 GTI in that the relay will only prime the pump on the first turn of the key, then after that it will not do so again until the ignition has been off for a while. Get the diagnostics wired in and check both the fault codes and the measuring blocks.

 

bin the carb heater relay, fit a GTI fuel pump relay

 

5 pin digifant connector:
red/green: cranking live - unused
red/white: fuel pump live - lambda/maf power
yellow/black: ecu relay - ecu and coilpack live
red/yellow: fuel pump earth trigger - AGU purple/white wire
red/black: fuel injector live - T10/14a fuel injector power

also splice AGU rev counter wire to the coil red/black wire, then add your converter under the dash inline with the wire to G1/12. i wouldnt advise putting it in scuttle/bay as i dont think they're waterproof?

you'll still need to run the diagnostic port wires inside, though plenty of grommets for that. speed signal and clutch switch may need coding out or run em in with the diagnostics wires

 

it'll have the CE2 fusebox in the 3.5 cab, and yes the MK4 rev counter signal is compatible with the mk3 clocks
only thing is you'll loose the mpg most likely, pretty sure the mk4 mpg signal isnt compatible with the mk3 clocks. no harm in trying!