JKubiak

OK - I need help. I've verified that I have voltage across the 5V fuse on my '78 and changed out the switch. Still no dash / gauge lights. Is this looking like a ground problem? What's the next test I need to do?

0Willcox Corvette

Did you check the right side of the fuse for 12 volts. I've seen many times where people test the fuse for continuity but didn't test to see if power was passing to the terminal. Corroded contacts for the fuse will cause this and the terminals in the fuse panel will need to be cleaned.

If you have, or if you do have 12 volts on the other side... Then I would pull the tach/speedo housing out of the car (easier then pulling the center dash cluster). and using a ground from somewhere else on the car, test for 12 volts on the power wire for the lamps... it's the 4th wire down on the connector, drivers side.

If you have power there, then use the ground for the lamps (top wire passenger side) in the printed circuit connector as your ground and test again. If you fail to light up then you've solved your question about the ground being the issue.

But.. quick question.. does your tach work? The tach shares the same ground as the dash lamps in your car.

JKubiak

I put the leads of the volt meter across the fuse and had 12V and even turned the switch clockwise and saw the voltage drop out. The tach is in deed working. In fact everything electrically is working. I'll begin the process of pulling out the tach/speedo and begin the testing process as suggested. Thank you for the input on this...

0Willcox Corvette

If the tach is working the ground is working..

What can take this out..

A short between the dash connector and the fuse, or possibly one of the pcb fingers loose on the back of the gauge housing where the connector plugs in. (speedo/tach or the center gauge bezel). I'd start by taking the speedo tach housing out and look at the connector that plugs up to this housing first...

Then I'd move to the center dash bezel and look for the same issue.

IMHO,

Willcox

JKubiak

I'm back troubleshooting this dash light problem and have done the following:

1. I again verified voltage across the fuse inst terminals to be 12V
2. Replaced the headlamp dimmer/rheostat switch
3. Tachometer is working properly - makes me believe ground should be OK on instrument trace board behind speedo/tach since this is shared
4. No breaks in traces or contacts on the speedo/tach instrument flex
5. Tested for voltage at the speedo/tach instrument flex dash light connector contact - showing 0.01 Volts - shouldn't this read 12 Volts?
5. Tested continuity between dash light hot side contact and instrument trace ground contact with the connector in place - this is OK

Am I correct in assuming that the entire instrument light circuit should measure 12 volts?

With what I've described above I believe I need to look at the voltage directly coming from the dimmer/rheostat switch. How and where can this be done? I currently have the speedo/tach out and have access to the interior of the dash.

JKubiak

One more question: when looking at the wiring drawings for the instrument lights there appears to be a splice where the power is distributed after the fuse. Where is this splice located? I'm thinking there may be a disconnect at that splice?

redvette78

I'm running into the same issue, replaced the light switch and still no dash or instrument lights. Did you resolve your lighting issue?

JKubiak

Yes, I got the fix after replacing the switch with no result. I found that the fuse box assembly was loose. Crazy as it sounds I re-seated the fuse box and tightened the screws. It fixed the issue. I couldn't find anything else creating the problem after tracing wires or finding a break. Perhaps a old corroded connection. Good luck.

henrikse

When you say 12 volts across the fuse do you mean you have negative from meter on ground and then checked both sides of the fuse and saw 12 volts/ Don't just touch the metal and each tab of the fuse but using point touch actual fuse clip as that is what can be corroded or open.

JKubiak

As I recall when tested I went fuse block to ground.