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

@rubjonny we finally managed to start the engine, it was the ECU Immobilizer Off not done properly, we got another ECU for testing and it fired right away.
After that i put back my ECU and it starts fine for 1 sec and then it turns off right away.
I removed the 2.0L 8V GTI from my MK3 GTI 1994, and will do a power wash tomorrow on the engine bay then place the 2.8L 24V AYL VR6 engine.

I have a some questions regarding the wiring harness.
After i removed the ECU and started removing the wiring, i noticed that near the ECU connector there is the right turn signal cable on the fender that is tied to the main ECU connector cable, also on that side i have the AC Pressure Switch (a 4 Pin connector), Carbon Canister, Outside Ambient Temp Sensor, (Old MAF & Airbox & Lambda Sensor connectors which i assume i should get rid of right ?).
in the middle of the engine bay there is the Rad Coolant sensor, then to the left the Brake Fluid level sensor, and the Coolant level sensor and the Wipers.

So just to be clear regarding post #1 as unfortunately i can't zoom the pictures of the stripped/chipped off cables (would be nice if you can add them somehow at full resolution so i can zoom them to check what you did, anyways - Following Post #1 i should:
Chip off that cable and remove the ECU Connector/It's wires from it and only leave what i need:
1. AC Pressure Switch (4pin connector) ?
2. Carbon Canister (2pin Connector)
3. Outside Ambient Temperature Sensor (2 Pin Connector)
4. Rad Hose Coolant sensor
5. Brake Fluid Level Sensor
6. Coolant Level Sensor
7. Wipers.

Am i correct ?

Then as for the other side, there are two rounded connectors:
1. The engine wiring and like 3 other connectors like Starter, VSS, Reverse
2. Lights and other connectors like the Fans and the Fans Activator Sensor on the Radiator, the horn etc.
So what about this left side, what needs to be chipped off.

My main concern is about AC as the car is climatronic, i would like to have a bit more specific details on what i need to do with it in order to keep its functionality.
On the engine bay aside from that 4 Pin pressure switch connector and the actual AC Compressor which does have it's 2 pin connector on the 2.8L engine harness already, it doesn't seem there is much to be done, i only get confused with AC from the Pins shown in post #1 like:
T10 Orange Pin 7 and Pin 8 ?
T14a pin 10 and pin 14 ?


Thanks in advance !.

 

Thanks @rubjonny
I started doing the swap since i collected 99% of the needed parts.
I am having an issue with the ECU, i sent it to a guy (business) for Immobilizer Off, it didn't work, told him, he said i need to have the car to verify so when i try i can test if i succeeded or not... whatever, today i sent it to someone else and he said that you need to revert the changes that the guy did to it's original state as we do the immobilizer off based on the untouched ECU. they kind off confused me and i got really angry with that all day as i feel like no one of them is knowing what he is doing. Will send the ECU to the first guy who tried doing so he can revert the original ECU condition then send to this guy who tried today as he said that once you do that i can do the mod without a problem.
Is that really the case as they said, what if the first guy who did the mod somehow lost the backup ?, he said he should have it as he keeps them all (after making a phonecall to him).
In a case where that backup is lost, what are the options? , is there an online database or can i simply grab a same engine code flash and flash it into mine ?
Or if all else fails, what would be the cheapest hardware/software to read ECU so i can backup myself and send to someone online to do the mods and immobilizer defeat, then flash the modded one myself ?.

Also is there any mod needed besides the immobilizer off, for the car to run fine if i keep the o2 sensors and SAI untouched (planned to mount the SAI Pump into the old-now empty place where the airbox used to be, since the 24v engine does have it on the driver side).
In this website: https://stancedubs.bigcartel.com/product/plug-play-mk4-engine-swap-harness they say:
"All VR6 swaps will need a "swap file" ECU reflash to prevent early rev limiter." - is this the same case for me as well into a MK3 GTI ?
I don't have/didn't purchase their harness but i just saw the note saying that and i was curious if it is needed to do that mod for the car to work properly ?.

and last - the fuel pump, is the MK3 GTI 2.0L 8V ok or i need to upgrade it for the 2.8L 24V ?,
If so what are the options, the one pulled from The VW Sharan where i got the engine from seems different and doesn’t fit.

 

Thanks, i got an ECU from same car model and same engine with immobilizer defeated, will send it so they can clone the eeprom where supposedly the immo code is stored and write it into mine, if that would work ? mine is 022 906 032 AS and the immo off one is 022 906 032 AR (both Bosch Motronic ME7.1 ).
For now i will attempt to keep SAI if possible since i can't mod stuff like that here until i get a flash read/backup so i can send to someone online for a mod.
I was just curious to know if these may causes issues with engine performance:
1. O2 Sensors, if not present will the car run at it's full potential besides having a engine light on or it will have power loss in general.
2. Carbon Canister = same question for it as 1.
3. I have the old ABS system on my MK3 GTI and the light comes on and off as it feels, a OBD scan shows like 00257 abs inlet valve front left and 00265 abs outlet valve front left, i was wondering what is required to upgrade to the Teves20 newer abs system that i can pull from a VW Mk3 Golf 1.9 TDI ? as lately it started to keep the light almost always on.

 

If it is a MK3 or "A3" chassis, your vehicle immo, will not be compatible with a PQ34 24v EA390 ECU.
There is a special technique used to De Immo the 022906032 ECUs and it varies if the ECU is from a PQ34 car or a PQ35 vehilce.
ME7.1 is a differnet matter usually.


I do prep these sorts of ECUs all the time mostly from EU territories. Mostly for classic car installations. I also own vehicles with those engines, including a MK2 (A2) Golf.

USDM LEV1 ECUs have a few considerations, around your readiness requirements.

 

Thanks, i think for now i am done regarding questions (until finish stripping down the wiring although thanks to your mk3 ce2 - fusebox chart/Faq, jt seems that there is answer for everything.

@Toyotec this is the ECU that came with the car.
It was a VW Sharan 2.8L V6 24V 2004 engine code AYL (attached picture of the ECU).
Hmm I can’t attach picture for some reasons..

 

So you are in the UK then?

 

@Toyotec I am from Kosovo if you know where it is.

So here is my ECU (022 906 032 AS):

and the one that i borrowed that is de-immobilized (022 906 032 AR) - attached in the pictures below.

I was wondering if it was meant for the same engine as mine or if it is possible to send this one to the guy who attempted to immo-off so he can copy it from this one ?

Also i do have a couple of new Questions @rubjonny

1. The engine bay wiring harness (O2 Sensors,MAF, SAI, Blue, Orange, Brown, White, Blue connectors etc) that i have is pulled from a Seat Toledo 2.3 VR5 because the 2.8L 24V AYL engine that i got from the VW sharan, the engine bay wiring harness was sold before i purchased the engine, i only had the engine wiring harness, so i had to find the closest to appropriate 2nd half (engine bay) wiring harness.
The wiring from the Seat Toledo VR5 does have only 2 Oxygen Sensors connectors (the 2 different connectors), i've seen some wiring harness have 4 Oxygen Sensors (2x per connector type)., should the car work fine with only the two oxygen sensors like one pre-cat and one post cat or whoever they are supposed to be placed.?.

2. I pulled the Teves20 ABS from a VW MK3 1.9 TDI completely with the MasterCylinder and the Vaccum thing that goes to the brake pedal for easier Installation, i took the wiring as well and as i've seen there were like 4 single pin connectors inside to the Fusebox, the main green connector, 2 cables tied that go under the rear sets for rear abs sensors, two on the engine bay for each fender for abs sensors and 2 cables to positive Battery Connector and a wire to earth under the battery tray. When you said ECU when we talked for the ABS, i assume that the you meant the ABS ECU, the one under the ABS pump where the main abs connector/cable connects, right ?

3. i did strip the wiring, it was a PITA to take the connectors out of the hole 1by1 and to remove that tape, tons of wires removed from the old ECU.
I put back the wire chipped off into the car so i can test it, Yes the car does start and work fine key on off, fuel pump/relay working fine etc, but i do have an issue with the instrument cluster, the red oil pressure stays always on even when igniton turned off, so does the red coolant level/high temp one and the clock and the mfa display(s) are not working at all.

4. About the AC, i think i found the two wires as they match colors with the T10 orange one, the Blue/Red one and the Green one, same colors on both MK3/Mk4 wires, on my MK3 GTI it was tied together after chipping the black tape off with the AC pressure switch and MFA outside temp sensor.

5. i didn't quite understand the section for the oil pressure and the coolant temperature sensor.
Oil Pressure: so the 24V ones won't work right ?, i will have to re-use/replace with the ones i had on the 2.0L 8V into the MK4 engine harness ?
Coolant level: so into this one i have two sensors into the thermostat housing of the 24V, one is brown and one is gray, what does each one do, and which one do i need to replace with the one from my 2.0L 8V GTI engine ?.

6. i have a brown/black wire from the radiator fan control module connector that somehow i lost track on where it used to be or may have been cut during the splicing.

Thanks in advance.

 

1. I will have to get back to this one later, after i am done with the MK3 wiring and have pretty much the rest working.

2. Thanks, i pretty much pulled the Teves20 ABS altogether with the brake booster, ABS ECU etc, including the complete wiring harness.

3. Are jumper blocks the ones above fusebox, there is a white, gray, green, blue and black ones and each have like 4-5 slots where you can plug single pin wires in ?
About the engine Kilometers, are they stored into the cluster or they do display what's actually in the ECU ?
MFA: you are right, i have this one disconnected, will give these fixes a try on the evening, as during the day i am working with clients, i am a car mechanic but wiring has never been my specialty but thanks to this thread that you did, i really learned a ton and getting so much more electrical work too thanks to you.

4. I left the MK3 coolant tank since the connector was already there, didn't bother messing up with it.
Will give the resistor a try so i assume i should place it between the T14a Pin 4 and the temp instrument cluster dash wire ?

5. will check their part numbers and write them here.

it's actually thin one, it comes from the radiator fan module next to the coolant tank and on the fender side and i have it cut there for some reasons, if that's an earth then fine, ill mount it under the battery tray.

Thanks !

 

Mfa and cluster fixed

its pin 4 brown/black, fcm part number 357 919 506 A

 

Trying to help out a mate that’s doing a 1.8t swap with a AWU engine harness and I have been cross referencing some of the wires as there is a chopped wire off the n75 valve and there for some reason is no map sensor on the harness whatsoever. The car I have done a swap too which was aum code had the map sensor on the same harness on the injector/tb side but this one has nothing at all!
Possibly removed before we got to it?
Have gone through what wiring we have and there is no plug anywhere.

We have two wires that we aren’t sure where they go off. They are:

Yellow/black this looks like it goes to the variable cam timing and possibly the n75 valve? There is 1end of the wire with 2x cut wires from it.

Purple/black

Is it possible to get a map sensor pigtail and pin it into the harness somewhere else and where abouts to?

 

The purple/ black wire is halfway through the engine harness. It almost is at the same location where the yellow/black glue conduit joiner is where it splits to go to the vvt and n75. When I had a look at the harness found that the yellow/black wire was tied up into the purple/black wire? Might have to do some chasing to follow it down and see where it goes.

Can’t find the map sensor at all in the wiring I got. The awu harness is off a new beetle. Managed to get a cut of wiring for it to rejoin into the harness. How would I go about wiring up the map sensor into the t14a? From what I’ve got it’s a 4 pin plug with 3x wires.

 

Is it possible that is this one mounted on the Air Intake Manifold on the MK3 2.0L 8V GTI, is it supposed to be like a security measure in case the the fan switch on the radiator fails so it turns the fans on ? Or it has different function ? Shall i bin it or keep it, if keep it, where would i normally place it on my 24V engine (attached picture below)


Also a couple of new questions raising as i WIP into the wiring part:

1. Coolant Temperature Sensor: Here i am confused a lot, like i previously said, on thermostat housing there are two sensors, brown and gray, i heard that one of them is for the car idle to be higher when the car is cold (cold start), is that correct ?
And the other one is supposed to be the temp level sensor, but the problem is they are both 2 pin connectors which does confuse me a lot with your coolant section as there is no MK4 4pin sensor, or is it placed somewhere else on the engine which i don't think i've seen any.
What am i supposed to do with the wiring in this regard (picture attached below)

Or try method 1 first with the resistor which as i understood, put it between the T14a Pin 4 and G2/3 wire am i correct ?

2. There was also a hose that came from the inside (heating) radiator to the side of the block which had a black 2 pin sensor which i don't know what it was supposed to be, i need to know whether i need to bin that wire and connector or not (picture attached below)


3. Oil Pressure Sensor: i installed the 1.8 bar (056919081E) white Oil Pressure switch and ran a wire from it to the G2/11 (blu/blk - low oil pressure warning switch) and the red oil light on the instrument cluster doesn't blink anymore when the car starts but it rather stays on now, instead of being turned off, have i done something wrong in this regard ?
Also the 2.0L 8V had another one on the engine head on the side, a black one with a black wire, was that supposed to be the G2/10 (yel - high oil pressure warning switch) or something else ?, If so what should i do with it on the 24V engine ?
Will have to remove the coolant and remove the front again with rad and fans as i don't have any clearance to put my hand and unscrew the tapped hole to fit the oil temp sensor for MFA.

4. VSS: what i did there is i placed a MK4 Sensor so the 24V engine connector can work (if that is supposed to be the right way).
I did run the T10 Orange Pin 6 blue/white wire to W/1 basically to Blue Jumper where there are 2 additional ones connected, one to abs and one to dash i assume, tested the car with one wheel lifted put it on 5th gear but the Vehicle Speed gauge doesn't move, have i done something wrong, was i supposed to run extra wires in order to have it to work, like chipping off the old connector or something, or just use the mk3 sensor with the standard connector but will that cause issues to the engine/ecu ? Sorry for asking too much but english is not my native and i am trying at my best to understand each section by reading it many times but there are a few sentences that i need to read many times to understand or don't get it at all and rather have to ask on a more noob friendly way.

5. RPM Gauge: as i understood, my MK3 GTI Cluster won't work without a 6 cyl to 4 cyl signal converter or would rather have to switch to VR6 clocks right ?.
As for wiring Orange T10 Pin 9 to G1/12 and it should work fine, am i right there ?

6. Post #1 Correction: On my AYL 2.8L 24V engine the T14a pin 9 is not an earth to battery or head, instead it's the Positive(+) power feed for coilpack, i struggled so much before asking on one of my first posts here to start the engine, i don't know how i accidentally put that wire to Positive to just give it a try and realized it was all that wire that gave me all the headache, without it the engine won't start, won't have spark.
If it was a typo, where am i supposed to wire it, on an ignition wire or ?

7. Diagnostics Port: Should the MK3 one work fine, just wire it to work with MK4 ECU or i need to replace it to a Mk4 one, would prefer keeping the original/it's original location if possible.

Thanks in advance !