fuel gauge problem
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Senior User
Joined: Jan 2011
Posts: 107
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From: North Georgia
fuel gauge problem
hey guys it been awhile since ive been on here but im back now 
.
so i just bought a 76 f100 4x4. there should be a picture in my gallery.
the fuel gauge is not working. i have checked the wire that goes to the tank and its good. my dad thought maybe it was the circuit board for all the gauges but i dont think thats the problem since all the other gauges are working. think its a hole in the float or something? just need yalls opinion on what to check first to save time and work, thanks.
also just ordered a 2 inch coil spring leveling kit and shocks. springs should be here today but shocks were back ordered until next week. so i will be having pictures of all that soon. got them from bronco graveyard.
.so i just bought a 76 f100 4x4. there should be a picture in my gallery.
the fuel gauge is not working. i have checked the wire that goes to the tank and its good. my dad thought maybe it was the circuit board for all the gauges but i dont think thats the problem since all the other gauges are working. think its a hole in the float or something? just need yalls opinion on what to check first to save time and work, thanks.
also just ordered a 2 inch coil spring leveling kit and shocks. springs should be here today but shocks were back ordered until next week. so i will be having pictures of all that soon. got them from bronco graveyard.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
When you say you checked the wire that goes to the tank, and found it to be good, what did you do specifically?
The proper way to check the wiring is to turn the key to ACC, remove the wire going to the sending unit, and ground it to the same point that the sending unit grounds. The gauge should peg to FULL. Is this what was done? If so, what were the results? If not, try it this way.
There's no way to check wiring visually. A multimeter is absolutely necessary to fix electrical issues, except in cases like this, where the gauge test can act as a shortcut.
The proper way to check the wiring is to turn the key to ACC, remove the wire going to the sending unit, and ground it to the same point that the sending unit grounds. The gauge should peg to FULL. Is this what was done? If so, what were the results? If not, try it this way.
There's no way to check wiring visually. A multimeter is absolutely necessary to fix electrical issues, except in cases like this, where the gauge test can act as a shortcut.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
When it comes to electrical, this will not tell you much.
Ideally you should be able to ground the wire to any metal (frame, bed sheetmetal, etc) but because of rust, road grime, etc this usually will not work. The sending unit pigtail should have two wires - one is the signal (which you will have disconnected), and the other is ground, which typically attaches to a crossmember with an eye terminal and screw. You can ground the signal coming from the truck to this location.
If the gauge doesn't peg, then something is wrong with the gauge or the wiring - but 9 times out of 10 it's because the rear crossmember has lost ground. Sometimes jumping to bed sheetmetal will correct the issue. Many times, the ground is gone, AND the sending unit is bad. However, either of these are very straightforward to troubleshoot; both require a multimeter.
If the gauge doesn't peg, then something is wrong with the gauge or the wiring - but 9 times out of 10 it's because the rear crossmember has lost ground. Sometimes jumping to bed sheetmetal will correct the issue. Many times, the ground is gone, AND the sending unit is bad. However, either of these are very straightforward to troubleshoot; both require a multimeter.
Thread Starter
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Senior User
Joined: Jan 2011
Posts: 107
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From: North Georgia
well i jumped the wire running from the tank to the front of the truck to the ground and the fuel gauge said full and when i unhooked it it dropped down to to about an 8th of a tank. when i turn the key off it drops to empty then when i turn it back on it goes to about an 8th of a tank. so it seems like its working now. before it did nothing. might be a loose wire or something.
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