[50droptop]

Ok, here’s the situation. Recently completed build, working the Gremlins out. Car has been converted to 12V (no haters), used a Ford voltage reducer from a 60’s mustang for the power feed to the oil pressure and fuel gauge. Oil pressure gauge worked great and was accurate against a mechanical oil pressure gauge as well. Fuel gauge never worked.

So while troubleshooting the fuel gauge, suddenly the oil pressure gauge stops working. Used a “D” cell battery to confirm the gauges, oil pressure moves fuel doesn’t.

Ok, so need a different fuel gauge. Scrounge through the spares and find a fuel gauge that reads with the “D” cell battery test. Replaced the gauge and decided to test everything before installing back in the dash.

Since the voltage reducer stopped working (could read 12V on 1 pole and 0V on the other), resorted to Runtz. Here are some photos of the “temporary wiring”. Red wire is from ignition side of terminal block to each gauge, black is ground back to body.

Here’s what the results are:

When power is applied, the fuel gauge shoots straight to “FULL”. With my volt meter, I’m getting 12V on the power side of the Runtz and 8V on the gauge side. Figured it was the sending unit, so I removed it from the tank, ran a ground from the housing to the body and moved the float arm.....no change on the gauge. It should be noted that I do not have the original 36 sending unit, but a NOS FAA-9275-B (52-54 Ford wagon). It was my understanding that later model sending units worked on the same principle as the early ones. The needle moving all the way to full is like the sending unit wire is grounded.

So my questions....
Is 8V correct for the power applied to the gauge?

Any ideas why the 60s mustang voltage reducer would have just stopped working?

Will the later model sending unit really work with the early gauges?

Any suggestions on how to move forward with the troubleshooting....I’m stumped.