electrical puzzle for experts

Gene Alvarez · 01-01-2005, 01:38 PM

We got this car with the sunroof motor missing. Found a used replacement and verified that it works by touching the leads to the battery. After installing the motor, the switch in the car makes the two direction control relays click, but the motor does not turn. The key is on ACC, not RUN.

With schematic in hand, there is power at the fuse (#1) and it is not blown. There is no power at pin 7 of the sunroof motor connector. This is the main power for the motor and comes direct and unbroken from the fuse. Since at pin 7 another wire branches out to power the latch release, checked operation of the latch release: it works. That means the wire from the fuse is not broken, right? Any ideas why there is no power to the motor?

Thanks,

Britwrench · 01-01-2005, 03:30 PM

In the ACC position the switch operates the system to partially close the sunroof for removal only. In the RUN position the system operates in the open and close directions. The system only operates with the sunroof installed (or you have to manually close the front microswitch) At a guess, I would think one of the microswitches is not working or the release cable is incorrectly adjusted. You will need to follow the technical bulletin for diagnosis as even though all the sunroof does is open about 2" Porsche managed to engineer (yeah, right) a system with three relays, switch, four microswitches and other bits that break.

The system is connected to the main harness as the closed sunroof automatically locks above 5kph...so if you just place the roof but don't engage the locking arms the system will drive the arms above that speed. This will stop the sunroof falling out at highway speeds. Usually.

Gene Alvarez · 06:57 PM

That explanation helps me understand how it's supposed to work since it's my son who drives the car regularly. I imagine that all that control logic is connected to the operating switch, microswitches, and relay circuit.

The mystery dead circuit is a different one, composed of a heavy (1 mm) 12V supply and gnd wires, that goes from fuse 1 through the open/close relay contacts to power the sunroof motor. What was confusing me is that the 12V wire continues on to the hatch release motor, which works. After studying the schematic some more I think I understand why:

The hatch release motor works like a self-parking windshield wiper. The switch on the console starts it, but a cam-interrupted parallel 12V supply keeps it going until it reaches a specific stopping point. This parallel supply comes from the sunroof motor circuit. I was seeing power in the sunroof circuit because it was being back-fed when testing the hatch release. Otherwise the circuit is dead, probably a broken wire.

That would also explain why the hatch does not latch correctly; the unlatch motor has no way to return to the designated latched position.

I've never seen a more complicated car. Certainly the opposite extreme of my 2CV!