Ford F-100 1981

What’s reason the gas gage isn’t working now is because the gas sending unit may have broken? Is the tank hard to locate?Is there possibly a wire that we number under the dash or a fuse that could have been blown that would make it ready empty when it’s full?

Taden - Thanks for posting here rather than via email.  I'll get this started and others will chime in.

Lots of things can go wrong with the fuel gauge system.  Here are some, but you can see the wiring here: http://www.garysgaragemahal.com/fuel-tank-selector--gauges.html.

Fuse: The gauges actually aren't on a fuse.  They are powered by the same circuit that runs the windshield wiper and washer, so if they work the gauges should have power.

ICVR: The fuel gauge, oil pressure gauge, and coolant temp gauges are all run by the Instrument Cluster Voltage regulator.  It can go bad, but if it does then all three of those gauges quit.  Are the others working?

Sending Unit: The sending units that go in the gas tanks are notorious for failing.  Sometimes the float leaks and sinks.  Sometimes the resistor goes bad.  But they fail frequently.

Wire: The wire that runs to the sending unit may be bad.  You didn't say which tank it is, but it could be a dark blue/yellow, yellow/light blue, or yellow/white wire.  Check it out for chafing because if it shorts to the frame the gauge will read full at all times.  Or if it is broken then the gauge will read empty at all times.

Hi Taden,

Glad you posted here, as you will get more input. I just went through this with my truck and the diagram that Gary linked is what you will need. You can test all of the wiring back to the sending unit (or units if you have two tanks) and test the ground like I did in my thread. You can also test the resistance between sender posts (10 ohms full, 72 ohms empty). In my case, the electronics were fine, but my brass float cracked, filled with fuel and sat always at the bottom of the tank. You can read about mine in my thread:

http://bullnose-enthusiasts.12971.n8.nabble.com/1981-straight-six-manual-4x4-project-tp1312p2894.html

As Gary mentioned, I am busy preparing for a trip so my apologies if I don't have a lot of time to post. I will try to help as I can.