Dvl1000

Hello all,
I have my 1988 S4 (auto) for 11years now and now have a big electrical problem. Relay X kicks out when I apply the brakes, and now wipers. This causes my brake lights, head lights, HVAC, cruise, wipers and driving lights not to work. It does not happen every time. I have checked all my grounds, and replaced relay X. Everything resets when I restart the car. Relay X does not always activate when I turn the key to ACC 2, just sometimes. I have looked at the wiring DWG and cannot figure it out. Could this be my ignition switch?

Thanks

David

Alan

Have you replaced the relay? It could be the ignition switch - but I'd start by swapping the relay (use the horn relay to start with).

Grounds is another possibility, in which case the one behind the CE panel is the most suspect.

Alan

dr bob

[Deleted incorrect info on X-bus relay. I was thinking the 88 is the same as the GTS, which I had some troubleshooting history with. Sorry!]

Alan

Actually on an '88 the brakes are supplied directly from the X bus terminal of the ignition switch, so it seems highly likely that you need to replace the electrical switch portion of the ignition switch mechanism, the relay wouldn't affect your brakes lights.

Alan

Dvl1000

Hello all,

dr bob, I do not understand the 50 circuit. I thought the ground was 31 and the starter has no problem starting so I don't think it is the solenoid connection. I will however clean the 14 pin connector..Thanks.

Alan, I think you are correct but would a draw kill the power from the switch?

I replaced relay X and checked all the grounds. It is very strange, relay X is suppose to be always on from power from ignition, so why does a draw (brakes or wipers) kick it out and why won't it kick back on when the brakes are released? Is it possible that some other relay is effecting relay X....the wiring DWG does not indicate this possibility.

This is my daily driver so I ran power from the buzz bar at the top of the fuse pnl to the brake switch. Now my brake lights work.

dr bob

[deleted incorrect information]

Alan

The X-Bus (X) in the diagrams is not supplied by the relay - its is supplied only by the ignition switch. This is what drives the brake circuit directly in your MY ('88). The X-Bus (accessory) is on before the ignition (15) circuit turns on, it is disabled when you turn the switch to starter mode.

The X-Bus relay is just a repeater of this circuit, with it's coil supplied by X and it's ground a fixed ground (31). Dr Bob - there are relays that work exactly as you describe - but this isn't the one.

Since your brake lights are causing the issue (and stop working) - the issue must be with the ignition switch (X output). Likely the contacts are damaged and have high resistance, in this case trying to drive a major load (like the brake lights or HVAC) can cause the circuit to drop out, while a much lower load - like just a relay coil - can work OK. Failures of the switch will of course affect the repeater relay too, but that is an effect not a cause.

I'd say a replacement ignition switch is the most likely answer. You may find wiggling the key a bit around may have some effect here too...

Alan

Dvl1000

Hi dr bob,

Thanks for taking the time. I checked the 14 pins in the 50 circuit, very clean. I also understand how relay X works now. I have a new relay in and I am getting different results everytime I start the car. My HVAC lets me know when the relay kicks out. Here are the strange combinations:
1)My HVAC usually works until the relay kicks out, headlights sometimes work, sometimes not when the HVAC works.
2) Driving lights work only when HVAC works.
3) Wipers sometimes kicks out relay and gives a brake light failure warning. (Remember I am not energizing the brake lighs through relay X anymore)
4) I can kick relay X back on while I am driving by turning my key to almost starter engagement.
5) The car can start with full functionality, some or no functions. (Each time is a surprise)

David

Randy V

How about an introduction thread with pics of your car to get you started off?

Dvl1000

Hi all,

I will replace the switch, thanks for the advice. I did try to shake it, hit it and sorry to say curse at it but the problem I am having is not related to large vibration/bumps in the road. Just sitting in my garage turning the ignition to ACC 2 back and forth can change the results.
Anyways, thanks for the advice, my brake lights are OK since the bypass and I'm getting use to driving in the dark with my driving lights as well I put rain X on my windshield.
I will let all know when the switch comes in and the results.

Randy, I think I have to purchase the membership for forum to post pictures. I think I will as the advice has been valuable. When I first got my car 11 years ago I was in the forums all the time but I have put the last 70 thousand mile on with only minor problems, it has 170 k on it now and I expect I will need this group's experience.

Thank you all