I can’t get an accurate fuel reading

April 1, 2009 | By Richard Prince


I installed a new fuel gauge sending unit in a cleaned fuel tank for a 1965 Mustang and I haven’t had an accurate reading yet. It sometimes indicates empty when it is 1/4 full and the old gauge was the same way. Even when the tank is full, it only registers about 1/4 full. Some folks say the problem is electrical while others say that the sending unit (a stock Ford item) is faulty. I need some advice as to how to proceed.


Given that the inaccurate gauge readings were the same before you had the tank cleaned and installed a new sending unit, I think it logical to assume that the problem resides in the wiring or with the gauge.

If you don’t already have one, get a wiring diagram for your Mustang. It will show you where the two wires connected to the fuel gauge go. One goes to the “constant voltage unit” and should bring reliable power to the gauge, while the other ultimately connects to the sending unit. Evaluate the wiring from one end to the other, paying particular attention to all connections. If the wiring is good, the gauge is probably faulty.