Are the circuit cards on dash clusters prone to go bad?
 

Yes yes I know it's probably a ground issue. But in this case I ran two ground jumpers from the case to a known good ground where my aftermarket gauges are grounded. So while I agree it's a ground problem I think it has to be the printed circuit card itself.

Still not all of the factory gauge lights work. Notably the left turn signal. All the bulbs are new. It is missing a single of the black bulb carriers and it's bulb. I tried to buy new ones but both rock auto and Orieleys gave me ones that were too small. I don't know if missing one of those I completed a circuit. Doesn't look like it should.

Also sorta unrelated. Should the turn signal switch itself turn off automatically when you make your turn. Or do the old cars require you to manually put it back in the mid (off) selection.

bulb
 

my 68 turns off automatically when completing a turn.
certain bulb missing will leave an open in some circuits.

Gerry

Well maybe that's it. Anyone know where I can get the correct bulb carriers? The AC Delco ones are got are close but wrong.

I suspected my turn signal switch may need to be replaced. It does make the signals work but doesn't automatically return to the neutral position.

http://www.bulbtown.com/

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The issue with the turn signal not canceling is usually a broken cancel spring which is very easy to replace. Get the new one at your GM dealer.
Once you get the turn signal switch in view you should easily see the broken spring.

A couple things to add.

I use some dielectric grease on the connector that connected the PCB. Those traces are delicate.
There should be one missing bulb from what I remember for the fiber optic cable to the ashtray.
When trouble shooting the gauge cluster do it on the kitchen table with a 9v battery and a 100 ohm POT. Draw out all the circuit paths so you can test each circuit. If you have the Rally gauges with the amp meeter don't put any voltage on that circuit.
You can use the 9v to test each light individually and then test the leads to the traces to.

Mine were all out and in a bag. I changed all the bulbs and just kinda guessed at it. I think I left the generator light out because I converted to an SI.

The plastic can de-laminated and then the copper corrode, otherwise only wear and tear from changing bulbs and unplugging/plugging the cluster in.

The circuit paths are very easy to map out if something isn't working. I've wired the oil, temp and GEN lights into the MegaSquirt EFI controller. The temp light comes on below 120ºF and over 210ºF (to know when I can turn the heater on or when the cooling system is being over taxed), and the GEN light comes on whenever voltage goes below 12.5 volts, which with the CS144 alternator shouldn't happen except in failure. And for the time being the OIL light is acting as a shift light at 5,200rpm, but eventually it'll be for oil pressure.

I'm guessing the GEN light is designed to work with a voltage regulator. Which it doesn't have at all. So it's probably reading zero voltage and coming on. I know the alt is charging fine because my timing light reads voltage. It was mid 14s last time I had it on.

If it's not a 1-wire alternator, one of the two plug wires can be wired into the GEN light to function as normal. The other wire is the voltage sensing wire used to regulate voltage.