Instrument cluster lighting cuts out after 15 to 20 minutes

[92EcoDiesel Jetta]

On my 92 Jetta, the cluster lighting always work when I turn them on, but would go black after about 15 to 20 minutes. Playing with the dimming rotary knob on the headlight switch does not help. It would always work again the next night, but only for 15 to 20 minutes. Turning it off and back on does not help. Does this sound like a flaky headlight switch? Anyone else with this problem before? I'll try to get a part number posted tomorrow.

[TylerDurden]

Sounds like the switch. Mine occasionally go dark and the dimmer is no help, but tapping or wiggling the switch sometimes brings them back. YMMV.

[CrazyAndy]

Did you test power to the switch to make sure the supply circuit isn't cutting out?  Could be a ignition switch concern, admittedly unlikely, but still rule it out.

[92EcoDiesel Jetta]

Did you test power to the switch to make sure the supply circuit isn't cutting out?  Could be a ignition switch concern, admittedly unlikely, but still rule it out.

The headlights work fine when the cluster goes dark. Can it still be power to the switch?

[92EcoDiesel Jetta]

Per Bentley current flow diagrams, headlight is not fused. Fuse #3, which powers cluster light and license plate light is blown. New fuse #3 did not blow but still no power to cluster lights. Buzzed out fuse 3 output wire to headlight switch (gray wire) and it was open circuit. Applied power to the gray/blue wire to the cluster lights through an ammeter and it went over the 20 amp scale. There's a short somewhere in that circuit. I hate  pulling the cluster on the Eco. I'll check the license plate light circuit for shorts first.

[Mark(The Miser)UK]

When first switched on does the dimmer work correctly?

[92EcoDiesel Jetta]

When first switched on does the dimmer work correctly?

Dimmer always works when the cluster lights work. The first time I turn them on from a cold start (next night), it always works. After 15 20 minutes it would cut out and won't work again till the next night. Been doing this for 3 months, until a week ago when i replaced the headlight switch with another used one, after which I have not seen the cluster lights again and I find fuse #3 blown with the other problems reported above.

[745 turbogreasel]

Previous owner tired of blowing fuses put a self resetting circuit breaker inline?

[DogDiesel]

Sounds like more amperage on the circuit than the switches can withstand.

Similar problem with my headlamps, after I installed zenon headlamps in my Mk1 Caddy.  Oh they were brighter, but my lights would go out after 10 minutes.  Flipp them to high and same after a period.

Installed relays for headlamps and problem gone.  There was nothing wrong with my switches.

Where could the extra amperage on the circuit come from?  Center console wired in, radio loads, and even shorting wiring. On the flipside, nothing burns wiring or popps fuses worse than a bad ground.

I'd check loads and grounds.

Wayne

[CrazyAndy]

Now that more info has been gathered, I am in agreement with Dog on this one.  Chase those loads and grounds for all involved circuits on fuse 3, because something is wrong in there.

[92EcoDiesel Jetta]

Haven't done any trouble shooting other than at the headlight switch and the fuse panel. Waiting for it to get warmer before tearing into anything. Here are a few pics of the wiring diagram. Can anyone tell me how Fuse #3 is powered? It is hot with key on but I can't tell from the wiring diagrams how fuse #3 get it's power.

Following fuse #3 in the diagram, it goes to lower case "v" to another page to a relay socket #10 for a fog light. In my fuse relay panel, the fog relay socket is empty.

[CrazyAndy]

It looks like it's powered through the headlight switch at first and second pull out position, which would make sense since that would act as a power for the supply side of the activator coil on the fog lamp relay, which looks like it's ground-side switched through the relay control circuit.  I'd pull out S3 and check which side is getting power, and then see if the other side gets continuity to the grey wire at the light switch socket.  If not, then check the grey wire with the green stripe.  If it's as it says in the diagram with regards to circuit continuity and not grounding out on the body, check your switch from terminals 8/30 and 9/58 because if it's getting 15 power with the key on when it's off, you might have an internal headlamp switch fault.

[92EcoDiesel Jetta]

Did some more testing:

1. Gray wire on headlight switch terminal 58e is hot only with headlight switch plugged in and turned on.

2. No voltage on gray wire if fuse #3 is removed.

3. Fuse #3's top contact goes to 58e terminal of headlight switch (gray wire).

4. Fuse #3's bottom contact is hot only with headlight switch on.

My Bentley does not have a fuse only wiring diagram for my 92 Eco Jetta and I can't tell how fuse#3 is wired and powered.

About a month ago, I soldered a very light gauge wire to jumper the gray (58e) and gray/blue (58b) in an attempt to by pass the cluster light dimmer circuit of the switch. The cluster lights worked for a few seconds and the jumper wire burned up right in front of my eyes! Good I was looking at the burning wire while it happened and it didn't start a fire!

CrazyAndy, what do you make of all this? Do you think the switch powers fuse#3? I buzzed the switch out with an ohmeter, and there is no indication that it does. Maybe the dimmer circuit portion of the switch is defective as you say. There are 3 terminals to the dimmer: 58e, 58b and terminal 31 (which is ground). 

[92EcoDiesel Jetta]

Weather getting warmer. 

My headlight switch is about $40 to $50 for a new one. Since I hate replacing parts by trial and error, I am bench testing the headlight switch (mine is the type with electronic control , not the rheostat type) with 0.5 A load of incandescent bulbs (a little more than what my cluster lighting draws). The dimmer works fine so far. I am going to let it run on full brightness for a few hours and see if it cuts out on the bench. The switch is wrapped up with insulation to make it run as hot as possible. If it does not cut out, the headlight switch is not the problem.

[92EcoDiesel Jetta]

Headlight switch bench tested for 5 hours without issues. Next will be pulling cluster to check lighting circuit.