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

Johnny did you mean G1/4 here?
Also, T14a/7 shows as ground on my diagram?

Also, a question on G1/8, it's a 20A fuse, is that not enough to run 2 lambdas, MAF, and leak detection pump?

Many thanks for all your input as always!

 

Ah, my apologies, I'm looking at the MK4 diagram so please disregard.

Good to know on the G1/8, thanks for that!

 

@rubjonny
I finally finished my wiring harness and everything works fine, i used a 167 relay since it was 40a rated for the ECU permanent live + Coilpack Power.
However i have a few before completing small problems.

1. If car stays for a while, when you go and crank it, i need to crank it for like 5 sec (it won't fire on first crank)., i turn the key back to 0 and crank again, the second time it will fire up right away. What could the problem be, is it possible that i need a 409 fuel pump relay like @Andy947 had that issue ?.
Was the problem similar?, once the engine starts, you don't have the issue anymore, turn it off, fire it up again and it will start no problem, the problem happens only if the car stays off for a longer period of time (haven't measured how many minutes or hours).
Or could it be the immobilizer of the MK3 causing that issue ?

2. The oil filter housing had a spare hole which i ended up fitting the Oil Temp Sensor, i didn't use a low pressure oil sensor at all since these engines do not have any, however when i check on the MFA, the oil temp always reports 160, is it possible that the sensor is faulty ?

 

Thanks a lot, problem is solved, relay 100 solved the problem. Car fired up in a sec.

Removed the Green/Black wire from the sensor, oil temp on MFA shows --- now, so hopefully that means sensor is faulty, will get a new one or grab one from the scrapyard and i think that should be it.

What i left for later though is the brake & clutch switchs.
Should bypassing them solve the issues, am i going to miss any functionality ?.
I have 4 spare wires from the old loom that i didn't remove for this purpose so i have no need to rerun them but instead make use of these by simply cutting them and wire them for the clutch and brake pedal switch(s).
1. The Red/Green wire F/5 if i am not mistaken ( ECU pin 32 (8v) as the fusebox FAQ says).
2. The Yellow/Black wire which i think is G1/10 (i have stickers on them with exact pin however...) - ECU pin 23 (4cyl), air mass meter pin 3 (8v)
3. The Black/White wire which i think is G1/7 - ECU pin 9 (4cyl).
4. The Red/White wire which is G1/8 - lambda probe pin 1 (post-96).

Should i use any of the wires from the existing brake switch for taillights connector or the second one has wires run separately ?

Also i remember we used to discuss about Outside Air Temp sensor and my car didn't have the wiring for it while MFA does have that function, i would like to add it since i have all these spare wires that i could make use of by cutting/re-wiring them to the fusebox area.
Which pins should i use for that, as the fusebox suggests many of them and not sure which one to use, fusebox FAQ says:
G1/2 - Brown White which i assume should be earth
G2/2 - Red White which should be the Temp signal to MFA cluster
am i correct ?

 

My MK3 had a 167 fuel pump relay already and it was causing me that issue that i mentioned previously, do you think it's possible that it was faulty ?, i have another 167 relay if that's the case which i used it for the ECU+Coilpack live feed ignition switched as you told me to do on previous posts, is 167 ok for ECU+Coilpack, or will the relay 100 do the job for that as well ?
Can you write some relay models that would do the job for ECU+Coilpack that i did.

Ok so i can simply bypass the clutch pedal switch like you mentioned on first post and i won't have issues with it right ?

Are you sure that you didn't check the wrong fusebox diagram ?
VW Golf MK3, CE2 Fusebox says what i mentioned previously, not what you just said or am i wrong ?

Ok i will do those two switches as well since that's what is left to be done anyway.

This should be easy, just to grab two wires somewhere outside.

I have an additional question, what would be the best 1.8T 20V engine code/model overall to use for a MK2 or MK3 swap, i am thinking of grabbing one while i can as they used to be like nuts but the demand is constantly increasing thus the price getting higher and higher every single time.
I also assume i won't need cluster swap as it's a 4 cylinder engine anyway.

Also an additional idea that came to my mind is that a VW Golf MK4, 3-door with a 1.4/1.6L petrol engine is usually pretty cheap as these engines are considered crap here, they are oil burning addict engines and they have no power, the idea is that you have a newer chassis + wiring compatibility for a swap, you have AC/Climatronic, power steering and ABS all by default pretty much, so i assume it would require less work compared to a MK2/MK3.
The only thing that im curious is what happens with ABS, will that require coding or i can simply grab the abs from the donor ?
Just wanted to get a brief summary of the swap requirements in general.

 

Hi,

I have overtaken a swap project. The wiring was a real mess and ive tried to sort it out. I have wired as The picture shows but the car wont fire up. I cranks but doesnt start. Fullt loaded battery, new plugs, smells fuel. You hear the car prime as you turn the ignition on. It started once but never again

Any ideas? Its a 1999 1.8t agu. The ecu has immo off.

In case the image dont pop up its here https://hellebjork.se/upload/files/Screenshot_2023-03-01-15-04-44-433.jpeg

 

Yes, it had a code for the carbon canister (not connected), low voltage (had a bad battery). Ive also changed the icm with no succes.

You can hear both the fuel prime and the throttle body when you turn ignition on.

The rev counter doesnt move when i try cranking it. Does that indicate crank sensor even though it has no code?

 

Thank you! Ive ordered one. I will update when ive changed it

 

Just wanted to come in here and say Thanks rubjonny and everyone else for all for this as it was a major help with my mk2 Jetta coupe AFP swap I’m finishing up. Just wanted to give a heads up to anyone using dual brake switches instead of the mk4 4 pin switch. I am running a Passat b3 hydro pedal assembly and the mk4 switch was too short to reach the pedal. Dual mk2/3 switches work no problem but the only thing is you need to use a clutch switch as the second brake switch. The red/black ecu wire spliced in no problem and worked normal but the yellow/white ecu wire will have a binary set to 1 with the brake in rest position and 0 when pressed. Running a clutch switch will reverse this so it is correct. Not sure if it was covered anywhere, but I read to use a second “brake” switch when running dual switches

Can’t wait to get this on the road. Using a clutch switch here has all my bits set properly!

Cheers!

 

haha oops I’m not sure how I missed mostly everyone else was RHD! Yep I’m LHD. Yes any switch that works the same will do, I’m using a mk3 clutch switch for the job and it works great. Thanks again!

 

Hi, brilliant guide. I’ve got my engine wired up and running, tho I’ve a problem with the fuel relay wiring (currently only runs when relay is bridged)
It’s in a mk1 with a CE1 fusebox, I had no wire in my D plug at pin 13 so crimped the trigger wire from the brown connector T6/2 to there.
D plug pin 26 is currently not connected
D plug pin 15 is also not connected to anything
It’s probably something very obvious, but I’m not seeing it atm. Please help! Thanks