Fuel gauge had been dead for a while before I took the car apart for restoration and rebuild. In the process I installed a new gas tank and gauge. When I finally got it running the fuel and temp gauges were working. After a brief time both quit. They did seem to be a bit shakey but worked. I did some diagonistics and determined that the constant voltage regulator was dead. .12 volts coming out of it. Replaced it with an electronic voltage reducer. Wired it in and have 12 volts in and 6 volts out. Ran ground wires to the dash. Gauges still dead. Grounded both gauge wires at the sending units and both gauges went all the way over indicating that the gauges were good and the wire to the gauges and sending units were good. According to the shop manual this would indicate that both sending units are bad. I am finding that hard to beleive but it is possible. Checked fuel sending unit with ohm meter and there is definately resistance which indicates that the sending unit is not an open on the circuit. Also ran a jumper from both sending units to a good ground to make sure both were grounded and still nothing on the gauge. Next step is to pull the gas tank sending unit and bench check it and try another Temp sending unit if i can find one in my spare parts. Any suggestions as to what I may be missing? The only other thing I will try is to jumper a ground from the gauges to a known ground but I find it hard to think the guages would lose ground even though it sure seems like a ground problem to me. And yes there is a new ground strap from the engine to the firewall which shouldn't affect the gas gauge. I hate electrical gremlins!!

My first thought would be to replace the "electronic" voltage regulator, and find an old resistance one. I've had a couple occasions where they didn't seem to function under load like they did on the bench-and it wasn't as overload either.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

I wondered about that myself but an article in the Early Bird Magazine a guy had problems with repo's of the old style and a new-old stock old style and he went to an electronic version and it worked fine. I just checked again and have 6 volts on the wire at both  gauges. All signs point to both sending units being bad. The gas tank sending unit was new with the tank. Not sure on the history of the temp sending unit but having trouble believing that they both failed at the same time. Possible that the old constant voltage regulator shorted out and burned up and took both sending units with it?  Plan on pulling the gas tank sending unit tomorrow and seing what I can find.

Am I the only one who ever finaly figures out what's going on and then wonders how he could have been so dumb? Pulled the sending unit and bench tested it with an ohm meter. Seemed to be working ok. Took flashlight and looked into the tank. Tank was almost totaly empty. I distinctly remember filling the tank with premium and adding Stabil when I parked it in the garage the last time. Apparently I must have driven it a lot further after I filled the tank the last time. Added 15 gallons of gas and the gauge now works. Won't be able to check the temp gauge untill I get the rear end work done and the weather gets better so I can drive it. The constant voltage regulator was the only problem all the time. The genaric electronic voltage reducer seems to be woking fine. Time will tell how it holds up long term.