deathbyaudio

Couple of months ago I bought a very nice 1990s 964 C4 coupe. Great cars - runs perfect. Last week I had some issues with the vent fuse and had to open the back fuse box and that was when I first noticed this mysterious additional control (see picture). It's a poti connected to the main electrical system. I asked my mechanic and he checked the wiring but didn't had any clue too. Seems that one of the former owners installed this one. As I don't see any function (tried it out) I just wondered if someone of you ever saw a modification like this and knows what it's about for?

cjoenck

What is it wired into? Can you trace the wire in the box and see what it connects to? A wiring diagram will solve the mystery.

deathbyaudio

Its connected to the main electrical wiring - without tearing everything apart I can’t see where it’s connected to. Just thought someone might have seen something similar and can me tell more about it.

Silvertarga

If it goes to 11 its a volume control for the exhaust

cjoenck

I thought it could the flux drive connector.

deathbyaudio

Well. It's not a Flux and not the volume for the exhaust... :-) Found another mysterious switch underneath the driver seat - seams it's somewhat connected to the control. But can't find any function for it...

Kappi2907

The red Cable suggest a high current (amps), as far as I know this cable is not stock and my advise is to investigate its purpose.
If the switch cable enters the motronic possibly an aftermarket chip (eprom) is installed with Hi - Lo address (bank) selection to host tuning mappings (e.g. Stock and High Ron).

cjoenck

Do you have heated seats or a seat heater aftermarket solution? High current cables to the seat could be for seat heaters that someone wired into the rear fuse box, possibly off the rear defroster circuit.
Just a thought....

deathbyaudio

That is a really good hint cjoenk - will check that out today! It might be that the control in the back is for the heat as well.