The top left light above the speedometer hasn't worked in months, but earlier this afternoon it suddenly did. Later tonight the top right which has worked consistently suddenly stopped working. The high beam indicator in the center has also been randomly working and not working. It seems there's either a bad ground or bad connection somewhere. Where is the ground located on a 78 98?

 

There's a ground point on the firewall above the passenger's side valve cover near the transmission dipstick. Make sure it's in good condition. There is grounding and bonding done in the dash too. If one is loose it could cause your symptoms.

 

Since the problem is limited to only a couple bulbs, I bet the bulb sockets are either loose or corroded.

A pencil eraser on the circuit board and a tiny blob of dielectric grease will more than likely fix it for decades to come.

 

x 2

 

Quite possibly. This is a dumb question but how do i get to it?

 

You take the dash apart. Literally. Process is in the 1978 factory CSM.

Once you remove the LH trim pad, you can then remove the speedometer lens and the speedometer head itself. You'll then see the plastic dash structure and all the bulbs. Since the structure would have to be removed to access the sockets from the back, this dash is designed to pull the dash bulbs out of the sockets toward the steering wheel.

The 78 Custom Cruiser had dash lighting problems and I didn't want to take the whole dash structure out to get at the sockets. I found a self-adhesive LED strip at Walmart, cut it to proper length, stuck it along the top edge of the plastic structure and wired it to the clock lamp. End of dash illumination problems.

 

I was afraid you were going to say that. I hoped there would be a faster trick but it seems not. Fortunately the fix ended up being a lot easier, the ground in the engine bay was very corroded. Cleaning it fixed the issue.

 

I'm sorry, but a bad ground in the engine bay isn't the cause of one lamp going out intermittently. Most likely is that you have loose or dirty contacts where the quarter-turn lamp holder fits into the circuit board on the back of the cluster pod. Bad lamps can be the result of a series of bad grounds, each one reducing voltage. It MIGHT be that the combination of the bad contacts at the lamp plus the one bad ground was an excessive voltage drop, and fixing the single point ground raised voltage enough for now, but don't be surprised if this isn't a permanent fix. I've had intermittent lamp problems on my 69 wagon for a while now, and it's the lamp holders.

 

This might help. Or not.

From the '78 CSM.

 

If you don't have it, you really do want the '78 CSM. In addition to the above, there are a series of instructions and diagrams on removing trim covers and taking the dash apart over seven pages in section 8A5-1.