jpoint

I have a project Targa that I just got running after 10 years of sitting (details at "964 Targa - 10 years in the desert"). Today I drove the car for the first time in the evening. When I turned on the lights the blower fan for the interior came on full blast. The control for the fan doesn't do anything so if the lights are off - no blower. When the lights are on - blower on full without any impact by changing the fan switch. Yes - the headlights work as do the fog lights, tail lights, blinkers and hazards. The fan starts as soon as you turn on the lights - i.e. the parking lights - and stays on when you turn on the headlights, or fogs or both. I suspect it's some kind of wiring bug from a prior owner years ago and might be tied to the light switch. Any suggestions before I go on the electrical safari?

cjoenck

Do you have access to the wiring diagrams? The fans are controlled by the CCU and as far as I know there is no connection between the light switch and the fans. I would start looking at wiring in the obvious places around the the fuse box, the light switch, and the CCU to see if someone cut / patched into the wiring.

jpoint

Thanks - I'll do that. It looks like the wiring behind the dash is the likely spot. At one point this car had a ridiculous stereo under a prior owner. I suspect the issue is related to that work.

jpoint

I'm only posting this in case someone else encounters this problem. It turns out that the harness on the back of the heater control unit and the ribbon wire inside the unit were unplugged. For some reason that caused the blower motor to come on when you turn on the headlights. It's almost like a default that turns on the defroster with the headlights so you can see in the dark even if the heater controls fail. Anyway - I pulled the control unit out and apart and plugged everything in and now the controls work and the headlights no longer affect the blower fan. I posted more details here:
https://rennlist.com/forums/964-foru...-garage-9.html