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Wiring dilemma: Fuel gauge

73F100Shortbed

That's how we roll!
5,937
320
NJ
Ok guys my truck had an electrical fire so I had to install a new wiring harness. When I was done the fuel gauge did not work. After some testing I realized that the power wire for gauges did not go to the icvr so I moved the terminal to a spot that would put power to the icvr. The gauge went to 3/4 but that didn't seem right. I put $20 in and the gauge doesn't move. I did some reading and realized there is a resistor wire but I cut out the original not realizing it was there. How do I fix all this and get my gauge working right? I put a voltmeter on the icvr and one side appears to show resistance and the other shows a fluctuation of 2 or 3 volts. I need to fix this ASAP. Thanks for the help.
 

73F100Shortbed

That's how we roll!
5,937
320
NJ
Thanks for the link. I assume that I'm somehow going to have to put a resistor in but I'm not quite sure how.
 

73F100Shortbed

That's how we roll!
5,937
320
NJ
In your link it shows an 8.5 ohm resistor from the ignition switch wire to the icvr unless I'm reading something wrong. I'm really confused.
 

fatherdoug

Tonto Papadapolous
There is another reference to a resistor in there also. I haven't done any trouble shooting on that system, yet. Sorry! Hope you get it figured out.
 

73F100Shortbed

That's how we roll!
5,937
320
NJ
Gauge works if I ground wire to sending unit. Pegs past full like instructions. I grounded the ground wire to battery just to verify my ground from sending unit is good. I'm guessing bad sending unit?
 

fatherdoug

Tonto Papadapolous
Sounds like. Mine hovered at 3/4 for quite a while before it finally gave up the ghost, but the float was only about 1/4 full of gas.
 
If you have dual tanks the S/U signal runs through that as well.

Think original harness..not some farmer method for this unique system.

The power signal sent to the S/U is a pulsing 5 volts....nothing else will work on OEM system
 
Last edited:

73F100Shortbed

That's how we roll!
5,937
320
NJ
I have one tank in the rear by bumper. I rewired the entire truck. I have everything hooked up right as per the instructions. If I ground the sending unit the gauge moves to full. If I take a test light to the wire near sending unit it pulses. I know the original wiring uses the 8.5 ohm resistor but my instructions as well as painless wiring shows 12 volts to the cluster. So do I need to try to find some kind of resistor in place of the original wire? I'm pretty sure the sending unit is bad since all the tests point to this and I ordered a new one but do not want to hook it up and ruin it if I really do need this resistor. None of what I did is some "farmer" method. The only thing unique is that they have 6 volt gauges in a 12 volt wiring system and every wiring harness instructions shows 12 volt power when you add new wiring.
 

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