Fw: Intermittent indication of headlamp/taillight out (1993 100/S4 Models)

[Huw Powell]

> Lights function perfectly. However, light out sign comes on
> intermittently even with no running/headlamps on, Not brake light
> related as braking has no effect on when signal comes on or off.
> 
> I suspect a ground fault ...maybe a bad switch? Help will be
> appreciated.

I don't know if this is handled the same way on a car as new as a '93, 
but the earlier systems run both L & R circuits through a comparator 
relay type thing, which then signals the OBC if they aren't the same.

If the lights are working perfectly, it is unlikely to be a bad ground 
or switch.

The relay thing is usually mounted in the aux relay panel above the 
driver's knees, though this is bound to vary from car to car.  There is 
information on how it works at several eurolight installation files on 
people's web sites (since it usually must be disabled when using relays 
to run the headlights).  Here is mine:

http://www.humanspeakers.com/audi/lighting-90.htm#autocheck

relative to an '89 90Q, of course.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/