I have a 65 and when I turn the ignition to on/start etc. the fuel guage will always peg out to full (trust me the tank only has a few gallons in it). Even if I disconnect the wire going to the sending unit, it still pegs out to full. Should I try grounding out the wire to see what happens? If it stays at full when grounded will it mean it's the guage or a wire leading from the guage to the sender? What do you guys think the problem sounds like? Any help would be great. Thanks in advance.
gas gauge problem
- Thread starter KreagerM
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reenmachine
Dirt-Old 20+Year Member
The fuel sending unit reads about 76 ohms of resistance when the tank is full and about 6 ohms when it is empty. If you ground the send wire, you'll have very little resistance, and the gauge should read empty. Don't leave the key on for long like this. Odds are it's not the wire or the gauge, but it's pretty common for the sending unit to go out with age. It's cheap and easy to replace.
iskwezm
10 Year Member
yeah,i dont think its the guage,there is a short to ground in the sender,i would read the resistance of the signal wire from the sender.Normaly when you ground the wire it will max the guage
reenmachine said:
I think you have it backwards. If you pull the feed wire from the sender and ground it to the body, the gauge will peg. If you pull the feed wire and the wire isn't grounding somewhere down the line, you will read below empty. I think the fellow has a cut in his sender wire between the gauge cluster and the tank and is grounding itself to the body. Those are a PIA to find.
reenmachine
Dirt-Old 20+Year Member
Yes, I had that exactly backwards. The higher resistance is at empty, so if you ground the send wire the gauge will indeed peg above full. It could still be a faulty send or a short anywhere between the needle and the gasjbuening said:I think you have it backwards. If you pull the feed wire from the sender and ground it to the body, the gauge will peg. If you pull the feed wire and the wire isn't grounding somewhere down the line, you will read below empty. I think the fellow has a cut in his sender wire between the gauge cluster and the tank and is grounding itself to the body. Those are a PIA to find.
Do a resistance check between the post on the sending unit and ground to see if it reads somewhere in the correct range.
Capt Dan
New Member
If it stays full even when disconnected, doesn't this rule out the sender?
Must be the wire is shorted somewhere. correct?
Must be the wire is shorted somewhere. correct?
Capt Dan said:
You got it. He stated that he removed the sender wire and it still pegs, so somewhere between the gauge and sender a wire is grounding itself out. I'd check starting in the trunk, then remove the sill plates, then the behind the rear trim panels and dash. I'm not too familiar with the early cars, but the 69/70 mustangs have a rubber grommet where the wire passes through the trunk floor. I'd suspect that grommet has a cut in it and has worked itself through the wire.
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