I'm trying to figure out if it's just a bad ground or something else. Only one of the gauge lights is working on my console gauges and the other lights aren't blown. Also, my temp gauge pegs when I pull the headlight switch sometimes. If I vary the dimmer, the gauge varies. Do you think this could be a bad dimmer switch, a bad ground, bad wiring connection at the console plug maybe or something else? The wiring is all in excellent unmolested factory condition. Same with the gauges.
I'm guessing the dimmer switch is bad, but I don't want to start changing parts if it isn't necessary. Especially with them being original.

Sounds like a ground issue in the console gauge area. I had the same issue when I pulled on the light switch my temp gauge pegged out, but my gas gauge went empty also. My gauge lights also were very dim then too. I fixed my grounds in the console and my gauges and lights work perfectly. I am sure if anybody else has ideas they will chime in.

I was just surfing around below and I found a wiring schematic. It looks like the lights are wired in parallel so if one works, they should all work. Must be bad grounds on the ones that aren't working. It's odd though. I looked at the harness and it didn't look like the console lights were wired together. It looked like a separate wire for each went to the connector. Might have been mistaken...