CraigL

1993 GTS (early) 5 speed manual

I developed an intermittent electrical issue today while running errands today. On leaving my second destination, I noticed the Stop Light Warning was lit even after I had tapped the brakes. In addition, the Radar Detector (cigarette lighter) was out as was the headlight motor. We checked the brake lights and none of the three were working.

I decided to head home before anything else stopped working.
These issues self corrected after a mile or two.
Nothing else developed over the next hour.
For the record, it was cold and wet day.
I have no idea if that is relevant.

I have been studying the electical schematics for an hour.

It looks like the cigarette lighter is fed off the X bus. I'm sure that quite a few things are fed by the X bus. Unfortunately I never got a chance to take an inventory of what else was affected.


I tried to trace the stop light circuits. They disappear into the bulb control unit. I'm not sure where this device gets its power. Since they dont work with the key in 'Off' position, the X bus might be involved.

The headlight motor runs into the Light Combination Relay XXIII-XXIV. It appears to be supplied by the 30 bus. But the relay looks like it works off the X bus.

Based on this, I have a few possibilities:

1) The X bus relay failed to energize.
2) The ignition switch failed to operate the X bus
3) Ground points need cleaning

Any suggestions/comments would be appreciated.

Thanks in advance.

ammonman

ignition switch going bad?

Mike

borland

Yes, X bus is fed by the ignition switch, so if your ignition switch is going bad, it could present the problem you describe. Next time it happens again, you might try wiggling the key in the ignition switch to see if the problem corrects itself.

Supply X relay is for the fog lights and DRL (if DRL relay installed). I think headlight relay only monitors X bus status.

Otherwise, it could be bulbs needing to be replaced in pairs.

CraigL

Thanks Mike and Borland,

I see now that the X bus is activated in the ignition switch and that the Supply X relay involves the fog lights. Since the issue involved more than the brake lights and all three brake lights now work, I suspect the X bus was not active. This means the electrical portion of the ignition switch is a prime suspect.

Anyone have further suggestions? Does anyone know if it is possible to start the car without a functional X bus?

CraigL

As usual, Bill Ball has had a similar experience.
You can read about it here. This forum and its inhabitants are an invaluable resource!

the flyin' scotsman

The main headlights and brake lights are switched by the ignition whereas the sidelights (parking lights) are not.

Good start to check the switch and related circuit/relay/fuses/