Pawned, I have been having similar issues as you but with both temp and fuel gauges in my '66 Fury. I made a 5v regulator using a 7805 chip but the gauges still don't work when hooked up to their respective senders. I borrowed a spare gauge from my brother to do some bench testing. His gauge reads 21 ohms resistance, which sounds like the correct range from what I read on a thread here.
I hooked the test gauge up to a 5v computer power supply and the needle pegged high as it should. I then used a variable resistor to simulate the fuel or temp sender resistance. Problem is, the test gauge reads half scale with 7 ohms resistance and full scale with 2 ohms resistance. These resistance values are quite a bit less than what the senders supply, which are on the order of 10 ohms for 'full' or 'hot' and 75 ohms for 'empty' or 'cold'.
I've been thinking of making a simple variable voltage regulator using an LM317 chip and a couple resistors (one of them being variable to adjust the voltage). I could try using a 7808 or 7806 but thought the LM317 would let me fine-tune my voltage to what the gauges need.
Thanks for your post. It has given me hope for getting the gas can out of my trunk.
