I'm branching out to all my resources trying to figure out the below problem, so I'll give it a go here too incase there are some electrical gurus here!


Right; I have a Mk3 with Mk4 1.8t, dash, and loom swap. I am running Mk3 door cards and so therefore Mk3 window switches too.
The passenger single window switch was easy. The drivers side however is proving difficult due to the setup of the Mk4 4-way window switch panel.

So basically, it's a Mk3 plug, and I'm trying to connect it to the corresponding wires in the Mk4 door loom. Basically what I am concentrating on is E81 and E40 in the wiring diagrams, they are the two front windows.

Mk3 switch:



Mk4 switch/loom:



So far I seem to have cracked half of it, I can get the switch to make both windows go down, but neither to come back up.
The illumination side of things is easy to forget about that, it's just the actual window control wires I'm struggling with.

So far I have;

Mk3 ws/ro --> Mk4 ws/ro
Mk3 br/bl --> Mk4 ws/gn
Mk3 br (pin 4 window earth) --> earth

These 3 connections work to operate the windows going down. I tried Mk3 ro/ge --> Mk4 br/bl but that makes the window go down again when you push up.
So at this point I started connecting ro/ge to random wires in the Mk4 loom and stumbled upon something very odd..
When I connect Mk3 ro/ge --> Mk4 gr/bl (which is the Mk4 illumination wire) suddenly the switch works 100% as it should going both up and down. At the time of testing, the headlight switch was unplugged and therefore the illumination wire was dead (it actually measures .01-.02v?). When you plug the headlight switch back in (whether it's turned on or off) the windows no longer work.

So I am completely confused as to how they are operating off what is effectively a dead wire??


As for the two diagrams though, the Mk4 diagram is confusing the way it only seems to have two wires for each switch, where as the Mk3 seems to have 3 going into each switch.

Any ideas? Much appreciated..

And some pics for kicks:




Full build thread if interested: Project Car: Mk3 1.8t