ctrain22

How are the dash lights grounded on the back of the dash? I mean, how is the dash grounded? Half of my lights work, and half don't. I think it's a bad ground somewhere, but how is the dash grounded? Are there ground straps or wires, and how do the connect? Anyone have a diagram of the printed circuit or picture of the grounds?

joe_padavano

On your 68, there are a number of stamped metal grounding plates that run between the various electrical components on the backside of the plastic dash. These plates are captured under the threaded studs that hold the dash to the lower cowl, providing the ground path. It is likely that one of the nuts on these studs has loosened up, preventing the plate from grounding to the cowl. The Chassis Service Manual has a picture of these ground plates.

a6m5zerosen

I'm an aircraft electrician and have repaired the dash lighting in many GM cars in the last 30 years. Usually, the best way to start out is to completely remove the cluster from the car. Remove each bulb from the back of the cluster & check for blackened or "silvered" bulbs. Replace the bulbs (I usually replace them all while I've got the cluster out, including the ones for the high beams, turn signal arrows, etc) and don't use the cheapest bulbs available-spring for the Sylvania long life bulbs-they're worth the difference in price. A more expensive option is to use the new LED bulb replacements-they come in all colors-the choice is yours. Make sure if your bulbs are in those plastic quarter turn receptacles that they lock tightly in place against the printed circuit board, and that their metal contact points are clean & smooth. Occasionally you'll run across a damaged circuit board, where the plastic is peeled away & the copper conductive path is damaged. If a new or good used circuit board is unavailable, these can be easily repaired with one of those kits you buy to fix a rear window defroster grid-the principle is essentially the same. I usually disassemble the cluster completely-often the lights are designed to illuminate the guages through a "lens', and many times I've seen these "lenses" completely coated in dust. You'd be surprised how much difference new bulbs and a good cleaning can make. Also, sometimes the rheostat in the headlight switch can develop a bad spot in the coil-type resistor the wiper slides over to brighten or dim the dash lights. Headlight switches are usually cheap & easy to replace, & if possible go for an AC-Delco original equipment replacement over the cheapo auto parts store version-they're worth the difference. Finally, here's a super easy electrical test anyone can do in thirty seconds-at night, with the engine running & the lights on, hook a good set of jumper cables from a good ground on the engine to a good ground on the chassis or firewall. Did anything change? Did the dash lights get brighter? If they did, the problem is the engine to firewall ground strap, ususally located at the rear of the intake manifold or the heads. Often these are corroded, broken, or missing altogether. New straps are cheap and available in the "Help!" section of any good parts store, usually in a red cardboard blister package. Clean off the two attachment points where you're going to attach the new strap with a wire brush, and don't use a rusty, crusty bolt for this-clean it up on a wire wheel or get a new one at the hardware store.

ctrain22

My frustration is that half the bulbs work, and half don't. Both signal indicators don't work, but the right half of the dash illumination on the speedo works but not the left. Can only part of the gauge housing be grounded?

a6m5zerosen

Have you verifed you have good bulbs? If so, use a jumper wire with alligator clips & give the cluster a good ground-see if that makes a difference. Clamp one end to any good clean ground under the dash & use the other end to test your cluster's various sections.

rcorrigan5

I had the same trouble with my turn signal indicators in the speedometer pod, and the problem turned out to be the pins on the back of the printed circuit - they were loose and had to be re-secured. A person real good a soldering can do that. Each pod is grounded to where it is secured into the dash at the two points for each pod, with the small screws. As well, there should be couple of short black wires that run separate from the instrument panel harness assembly. One runs between the first and second pod and the other runs between the second and third pod (if the third pod has a clock or t-t-t) to enhance grounding with all of the pods. The black wires are attached where the pods mount into the dash with the little screws. It could be your dash lights aren't working properly because the ground isn't good. Otherwise, it might require some printed circuit board repair or swapping out of old for new llight bulbs as mentioned previously.

ctrain22

Well, it turns out it is the circuit board pins. Two pins are broken. Does anyone sell new circuit boards or is repairing the only way to fix?

Lady72nRob71

I have never seen replacement boards, BUT perhaps someone on this forum might have some old junk gauges that would be worth getting just for the boards.

If you know a friend who is handy with soldering irons and PCBs, let him look at it and see if he could repair it (depends how had the damage is. If just the electrcal connection is broke and the pin is sturdy in the board, then it should be repairable.
I have worked wonders on PCBs before (part of my career...)

ctrain22

Just the pins are the problem. Two are broken off, one a liitle loose and the last is solid. The rest of the circuit board si fine. I am going to see if I can find am electronics place locally to see if they can repair it.

rcorrigan5

Here's how I fixed my loose pins. I'm not a solder jockey so I tried an alternative method which worked great, although you still have to be real careful. I went to a model airplane sotre and bought some very small (2mm) fine thread screws. They were just the right size that they would self thread and screw into the back sides of the loose pins (the pins are hollow) and snug them up against the printed circuit, with the head of each screw against the back side of the printed circuit board. All the functions in my dash pods work now.

ctrain22

I saw your post about your fix on another post and give you credit for the ingenious repair. I was going to try that route, but first searched for a local printed circuit repair place and found one right here in town. He never repaired one like this before, but said he would look at it. I brought it to him, he showed one of his workers, and 15 minutes later and $20.....fixed.
1201090821a.jpg

Lady72nRob71

NICE!!!!!!!!!!
Cheap and easy, too!
Now take a pencil eraser to the bulb contact pads to shine em up and polish the contacts on the little sockets. You should be trouble-free for many years.

ctrain22

Replaced the bulbs and sockets for safe measure, and we have lights! All my dash lights are working. It looks like Xmas now.

rcorrigan5

That's a slick repair! In the end that looks like a better repair to me than what I did. Glad to hear all is up and running the way it is supposed to be!
Randy C.