Rocket Rob

Everyone,

I'm having a problem with my 1990 964 Cabrio. The cab roof light in the dash clock will blink at random times while driving when the roof is up and locked. The light stays off when the roof is down. Using the wiring diagram and Adrian's book. My friend and I have spent two Saturday's trying to isolate the problem without success. I'm hoping you can help me.

I'm beginning to suspect that I either have an intermittent problem within the cab roof control unit itself or a broken wire in the harness. What have I overlooked?

What works
- The roof moves up and down without problems.
- The roof locks and unlocks ok too

Diagnostics performed
* Checked adjustments of microswitches on cab roof motor.
* Roof lock microswitch continuity - works when manually toggled
* The Cab roof motor microswitch continuity - works when manually toggled
* Cleaned the contacts to the cab roof control unit & T35 connector
* Shunted the roof lock microswitches - dash clock continues to blink randomly
* Shunted the cab motor microswitches - dash clock continues to blink randomly
* Disconnected motor lock sensor power (T35 pins 1 & 7) - blinky light
* Grounded microswitch pins on T35 pins 2, 3, 4 - blinky light
* Grounded T35 pins 1 & 7 - blinky light
* Grounded T35 pins 2 & 4 - blinky light
* Disconnected pins in T35 sequentially. All had no effect (continued blinky light) except pin 3. When I disconnected that one, the light stayed on solid.
* I checked the voltage on T35 with the ignition off and with it on. All pins had zero voltage, except pin 1 which had battery voltage (12-13v).

Thanks in advance

dfinnegan

Rob, I had a strange problem with my master alarm light (the '!') coming on by itself randomly. I finally traced it down to a Central Informer connection. I discovered that I could reach under the dash while driving and tug on the wiring harness and get the light to go on and off.

When I pulled the CI and disconnected, and re-seated, the two plugs the problem went away.

Probably a long shot. Good luck finding the culprit!

Gus

I am not sure if this is the problem or not - but you may want to check the wiring in the top itself. The wiring to the top micro switches runs along the right side of the top - in a position just aft of the right passenger window top right angle ( inside the hard cover) the wires make a 90 degree bend and are constantly flexed as the top goes up or down. It is at this point that the wires will break due to fatigue. You may find that your wires are on the verge of breaking / broke but still offer a little contact so the light comes on then goes off. Does the light blink in a consistent pattern or is it very random? Once the wires break the light will stay on all the time -
Just another place to look -

Rocket Rob

Thanks for the idea. I'll check that this weekend.