A2 - Instrument panel lights, gauges problem

[gamber]

I am at my wits end - damn VW electrics!  I am so far in, I cannot give up.

Car
1985 Jetta Turbo Diesel

Problem:
Instrument panel lights and instrumentation work great, until I turn on the headlights and the ignition is turned on.
With the ignition in the on position (running or not) the instrument panel lights go off, the clock dims until it goes out and depending upon the position of the light dimmer switch, the tach will reduce to either 0 or roughly 50% of its usual revs.

Diagnosis
Appears to be a lack of voltage to the instrument panel when both the lights are on and the ignition switch is turned to the on position.

Actions attempted to resolve:
- replaced the headlight switch (no change)
- replaced the ignition switch (no change)
- checked the voltage regulator (a steady 9.9v)
- replaced the instrument panel (no change)
- ran an additional ground from the battery to the grounding point beside the fuse panel (no change)
- removed and reinstalled the terminal connectors to the grounding point (no change)
- disconnected, inspected and re-connected all connections to the fuse panel (no change)
- tried to run a new ground to the white (right side) instrument panel harness (no change)
- tried to trouble shoot with the headlights connected and not connected suspecting a short (no change)

Long story short - I have tried all I can think of and yet no resolution.

Any further ideas?

[the caveman]

You can try the "x" or 75 circuit relay. Don't actually think it's that, but the fact that it works when not running is a clue. When running did you check the voltage at the cluster?

[The Mad Hatter]

Have you checked your alternator?  I was having funky cluster issues, and had my alt. checked.  It was not putting out enough voltage.  New alt solved the problem.

[the caveman]

also check the ground from the body to the battery

[gamber]

Thanks for the ideas.
Alternator
- I have checked the alternator and installed a new voltage regulator
Grounding
- I have also checked the ground to the body and have added an additional wire from battery to the grounding block.
I guess it would be safe to check all the primary grounds however.

[rubadubdub]

i had a very similar problem to you.  With the engine off and headlights on the dash lit up, with the engine running the dash lights went out.  Some wierd stuff happened with the dimmer switch as it would change the output the voltage regulator gave depending on its position.

In my case it turned out to be a small tear in the plastic circuit board right next to the voltage regulator.  I think theres a picture on here somewhere of it.

My advice would be to take a very close look at the circuit board and make sure its not damaged.

I dont envy you having all this to work out.  I took my dashboard apart about 10 times before noticing what had happened and checked virtually everything on your list, extra grounds etc etc..