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Unread 09-09-2014, 04:05 PM   #1
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1979 FSJ Cherokee 
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Fuel tank sending unit no ground wire?

Any help appreciated. Replaced sending unit, and still no results. Tank show dead empty. Does the sending unit need a ground wire? The original sender did not have a wire for ground either.
Thank you

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Unread 09-09-2014, 10:12 PM   #2
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It wouldn't hurt anything to add a wire from the sending unit to the frame to rule out the possibility one way or the other.
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Unread 09-11-2014, 07:41 PM   #3
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Might depend on the year. If you have a metal tank, it probably doesn't need one. My '90 has a platic tank and has a separate ground wire. I don't think that is the problem. Bad ground would peg the gauge. I think your problem is on the + side of the circuit. Open + wire or bad dash gauge, maybe?
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Unread Today, 04:04 AM   #4
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You might have a poor ground path. The gauge reads empty at around 70 Ohm and full at around 15 Ohm. If you take off and short the sender wire for a couple of seconds you should see the gage rocket up.

If you have an open circuit you will see empty.

Two possibilities:

- poor ground - add a secondary ground from sensor to frame or preferbly to a black ground wire that is continuous to the back of the instrument cluster.
- duff sensor or one with the float full of petrol or sunk - best way to tell is to get a multimeter and measure the resistance at the sender.
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