Gauge cluster illumination

[91merc]

I got an 85 GM and a PO wired the radio directly to the battery, and I'm in the process of properly wiring it back in. I also have no gauge illumination, and I was wondering if the gauge illumination ran through the radio wiring like on some cars?

[gadget73]

No, but there is a connection from the dash lights to the radio. If someone shorted it you may have just blown the fuse. Should be the only 3 amp fuse in the box.

[91merc]

All fuses were good on the under dash block, got the cluster somewhat pulled out and the bulbs didn't appear burnt out, haven't tested for power because it started raining before I could get the speedo cable off to pull the cluster out completely

[91merc]

I just checked and none of the bulbs are burned out, I have the check engine and Amp lights but no gauge illumination, could the circuitry in the cluster be bad?

[sly]

The power for illumination comes from the headlamp switch. This is a known failure point with the massive wire harness liking to melt in various ways. That could be the issue.

Should be the brown wire.

[friskyfrankie]

The power for illumination comes from the headlamp switch. This is a known failure point with the massive wire harness liking to melt in various ways. That could be the issue.

Should be the brown wire.

+1. I would not only check the switch but also the connector as they tend to get "crusty". Examine the connector and the back of the wires going into it. A common theory is that Ford used thinner wires than they should have and this is a "burn out point".

[sly]

The quick connects used get crusty and create resistive connections and then get hot and just get worse as the plastic harness degrades due to the heat. This is the reason for the relay mods that dump all the current through a relay instead of the switch.

[91merc]

Well I have headlight switched power at the pigtail that goes into the cluster.... Now what?

[sly]

check traces on the cluster. Check for cracks and oxidation on the connector. May just need a good cleaning. May have a bad ground for the lights. Check both ends of the circuit. I think there's a couple of grounds coming out, but just follow the traces. They're pretty easy to follow. If you run across any cracks, defroster trace repair kit works (or conductive epoxy) pretty well if you're not real confident in soldering skills since the film will melt pretty easy.

[VicCrownVic]

+1, traces are easy to follow. Look for traces that have lifted away at the connector. If the cluster has been out previously, it's a possibility.

If you have a multimeter, check for continuity from the correct cluster connector pins to each light socket unless you find an obvious break like Sly described. If you need the pinout I can get it later if I remember, or someone else might have it already.

[91merc]

What's the best way to fix lifted traces?

[VicCrownVic]

A question I would be interested in hearing suggestions on as well.
I used some glue but don't remember what I used. Super glue might react weird with the materials involved. If its a trace where the connector connects you will have to scratch any glue off that gets on the contact surface.

[91merc]

Found 4 traces lifted off the membrane and one is kinda torn up, are new membranes obsolete or is repair pretty easy?

[91merc]

Will a Cv cluster swap into a Merc or no?

[sly]

cv/merc clusters are very different.

A little dab of rubber cement, contact cement (non aerosol... good luck with that), shoe glue, some other flexible adhesive should probably work just fine. As long as the trace is all there and not torn, you should be able to fix it pretty easily just by laying it flat and putting some stick-it-down goo between the trace and film backing. Just be sure the contact area stays clean on top.