While on a cruise last week, the temp and fuel gauges on my '64 Valiant quit working. In a half hour, they switched between off and normal several times before they finally quit and stayed off. Everything else is acting normally.

I suspected a bad internal 5 volt regulator, so I replaced the fuel gauge with an extra I had squirreled away. No success.

Conclusion: I either have a second bad gauge, or it's a different problem. I have yet another gauge, but before I tear the dash out again, does anyone have any other ideas?

I'd check for a loose or oxidized pin on the PC board. You might try just gently unplugging and replugging it back in w/o removing the cluster - often that's enough to make a good connection.

I checked the connection and it was fine. The pins are tight, the board is in excellent shape, and I had 12v at the pin that powers the gauges at a time when the gauge was not working.

Has anyone noticed intermittent operation of the gas gauge reading that did, or did not affect 5v power to the temp gauge? The service manual doesn't show a schematic of the gauge and 5vdc limiter, so it's hard to tell what failure it might be having.

I'm not ruling out a bad/corroded connection, but from what I can find, it doesn't seem likely

If both the temp and gas gauges went off together, it pretty much it has to be an open in (1)the limiter's power feed, (2)inside the limiter itself, or (3) you must have multiple poor connections (very unlikely). If it lost limiter ground, the limiter would turn on all the time and you'd have 12V at the gauges and they'd both peg. If you lost a 1 sender connection, would gauge wouldn't read, but the other would be fine.

You need to make sure 12V is reaching the gas gauge. The pin's joint to the PC board is a weak point that I've seen crack and make an intermittent connection - having 12V on the female plug and pin is no proof that the 12V reaches the board and then the stud on the gauge. If you see 12V on the gas gauge's stud and nothing on the gauges, then you know you have a bad limiter.

On the '65 Baracuda with a similar problem I put in a jumper from the harness direct to the gauge as a bypass as a temporary bypass for the bad pin.