on my 78, the lights for the speedo and tach do not function. the lights for the turn signals, high beam and parking brake all work fine, although the high beam light is functioning backwards which never happened before (light is on with low beams, off with high beams). all the lights on the center gauges work fine. i've checked bulbs and fuses and they are ok. ideas?

 

I would pull the speedo-tach unit out and inspect the flex. circuit on the back for a burned trace or other defect. Make sure the connector is plugged in tight.

 

i tried removing the unit, but it looks like i have to remove the steering column to get it out

 

Just rem. the 2 lower column bolts below the dash. This will let the column drop 2 inches...

 

everything on the back looks fine. some of the lights are missing but that's about it

 

help

 

sorry, no help for you...nice avatar though.

 

one more try

 

Track down the ground for the speedo and tach, make sure its got a good connection. I too had the same issue on my 69. The "bright" light would come on reverse from what it was supposed to, and the lights didnt work inside the tach and speedo. Turned out the person who owned my car before my crushed the ground connector in the sterring column mount instead of connecting it.

 

all my wiring is wrapped in electrical tape. i'm replacing all the tape with cable ties so it will be easier to trace wires. is the black wire the ground, or is that a bad assumption?

 

still no luck. i couldn't trace the ground wire, so what i did is insert another grounded wire into the back of the harness. still no lights.

 

Do the lights in the center cluster work?
All the dash lamps come from the headlight switch.
The headlight switch has resistive wire coiled up at the front.
Sometimes it falls out. (Did on my 76 any)
Looks like a spring.

 

the center cluster works fine, or at least it did before i ripped everything out to trace the problem. right now they are disconnected.

 

You mentioned that you checked the fuses. Did you check all of the fuses, or just the ones on certain circuits? When a fuse goes out on these cars, there are times when it will make other circuits misbehave, not just the circuit to which the fuse belongs.

For example, when the fuse for my power window circuit went out (I had a '75), the "bright" hi-beam indicator would light. It took me awhile to figure that one out. I had a power window switch that went bad, and so if I pushed it too hard to close the window, it would blow the fuse. The "bright" indicator would catch my eye, and I would hunt for a problem in that circuit, without immediately realizing that my power windows were no longer working. Very strange. A friend finally suggested to check my other fuses. It got to the point that whenever my "bright" indicator came on when it wasn't supposed to, I would change the power window fuse. I didn't figure out the real problem until the window switch got bad enough that I could smell it.

 

well, now that you have mentioned it, when i checked the fuses, the stop light fuse was burnt so i replaced it and it went again sometime between then, and today when it burnt again. I'm using a 20a fuse on the stop light circuit. that is proper, isn't it?

 

I'm not sure what fuse is proper for that circuit in a 78. The owner manual should have that information. It's probably a good idea to verify the correct fuse though. Don't necessarily just replace a fuse with the same value of fuse that is already there. Previous owners are not always rigorous in using the proper fuses.

If you don't have an owner manual, I can check my various manuals when I get home. I usually consider the fuse box labeling and the owner manual the best source for that information though.

By the way, did replacing the stop light fuse fix the problem (at least until the fuse went again)?

 

I remember at one time GM would feed the dash lights curcuit through the parking lights curcuit. So, if your parking lights fuse blew, the dash lights would go off, alerting you to the problem. This was on a '70 Nova that I discovered this.

 

You can find diagrams for an 80 at this site. I think the cluster wiring is the same...

http://iotech.no/corvette/technical/...tics/index.htm

I think if your center cluster works your tach and speedo cluster should also work. I had a similar problem. The copper stip where the connector went into the board had come loose and shifted. when the connector was plugged in it wasn't making proper contact with the board.

I assume your head light switch works. when you pull the **** out the center cluster lights up....correct? This action should also light up the tach/speedo cluster. Does your dimmer switch work on the headlight switch?...the coil behind the headlight switch trim piece sometime severes causing the lights not to work....some bubba the wiring to the center cluster so it lights up...any bubba wiring in your car???

The ground for this circuit is located up on the inside panel near the headlight switch. If you lie on the driverside floor and look up you should see the ground on the frame near the door pillar.

You can also check for power to the harness for the tach/speedo cluster. Get your self a cheap test light. attach one end to ground. Touch the other side to the pins on the harness connector one at a time...pull your headlight ****...watch for the center cluster to light up as well as the test light. You can no damage anything by doing this. If your center cluster lights up and the test light lights up you know you have power to the speedo/tach board and the problem is in the board...the ground ...or the connector. If the center cluster lights up but not the test light...keep trying the other pins just incase the power is feed from another wire (highly doubt it though).

If you do find the center cluster lights up while doing this test but no power to the pin your test light is in trace that wire back...your problem should be somewhere along the the line.

Jim

 

I would also check the circuit to your high beam switch. There could be a broken wire there. With a new fuse. Headlights on...using the high beam switch...does a fuse blow??

If this problem is related. You can check. I would unplug the highbeam switch and see if your speedo/tach lights go on.

Jim

 

I have the opposite problem on my 80. The speedo and tach light up but no center lights, ie High beem and turn signal indicators. Just got failed for inspection on this. Any ideas not covered here already??