Wire harness question
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Joined: Feb 2005
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From: South Dakota
Wire harness question
I have a 77 Ford F-150 4x4 and im trying to get my rear gas tank sending unit to work so i strip'd out the old wire harness that shoots towards the back and believe me it was junk, wires cut here and there so i found another donor wire harness but now i cant seem to get the gas gauge to work and my truck has a gas tank behind the seat and an aux and main switch and i tried both but none worked. Do you guys know if there's something else that needs to be changed like a fuse or something, the back wire that plugs into the sending unit in rear gas tank is grounded and there's nothing wrong with the donor wire harness so i dont know any idea's would help.
thanks
thanks
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From: Virginia
First go back to the tank and take the sending unit wire off the sending unit. I am not sure in 77 but in the 80's it was a yellow/blue or a blue/yellow.
With the keyswitch in run, engine off, take this sending unit wire and ground it to a good ground. The fuel gauge should swing full scale empty or full. Then take the wire off ground and let it hang in the air. The gauge should swing full scale the opposite direction. If this works, then you know the wiring and the gauge are all working, and you have a problem with the sending unit, or the sending unit ground if you used a good known ground during the test.
If this test doesn't work, then work your way back up to the instrument cluster. You can do the test right at the cluster if you can find the correct wire that goes to the sending unit. And you can use this test for the temp guage also, you just ground and unground the temperature sending unit wire the same way.
With the keyswitch in run, engine off, take this sending unit wire and ground it to a good ground. The fuel gauge should swing full scale empty or full. Then take the wire off ground and let it hang in the air. The gauge should swing full scale the opposite direction. If this works, then you know the wiring and the gauge are all working, and you have a problem with the sending unit, or the sending unit ground if you used a good known ground during the test.
If this test doesn't work, then work your way back up to the instrument cluster. You can do the test right at the cluster if you can find the correct wire that goes to the sending unit. And you can use this test for the temp guage also, you just ground and unground the temperature sending unit wire the same way.
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