I'm working on a 1970 M151A2 military jeep and the fuel gauge, I thought, was bad so i bought a new one for it and it acts the same as the old one. As soon as i turn the switch on, (it has a switch instead of a key) the fuel gauge pegs out totally full right away. So i thought if i unhook the wire that goes to the sending unit straight off the gauge and it still pegs out the gauge is the problem but both gauges peg out the same. The only wires the fuel gauge has on it is the sending unit wire and a wire that gets 24 volt when the switch is on, and they ground it through 2 nuts on the back that holds a bracket against the instrument panel to hold the gauge in place. So, i'm not sure if 24 volt just works differently that i'm not aware of or what's going on. and i know for sure that the wires are hooked up correctly. Any ideas are welcome.
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Anyone fimiliar with a 24 volt system, '70 jeep
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Mark_88
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Not too much difference between them from what I understand...they are essentially wired the same...if a gauge is pegging out but everything else works properly then I'd suspect the gauge wiring is wonky...like it is shorting out somewhere...trace the wires from the sending unit to the gauge and you will probably find a loose ground or bare wires are rubbing against metal somewhere...
I had the sending unit wire unhooked from the gauge and it pegs out. With just power and ground to the gauge is when it pegs out without the sending unit wire hooked to anything on either end. and it'll be hard to trace wires on this because every wire on the entire thing looks exactly the same, all black and bigger than a "normal" car wires and they just have small metal tags on the ends with a number stamped on it.
Mark_88
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Hmmmm...military application...that makes it harder to trace...
But that could be normal...with power and ground without any resistance as is built into the sending unit it would peg out...like hooking a volt meter to 110 service with it set at 10 volts...
The gas gauge works as a potentiometer and provides resistance according to the level of gas...
If you haven't already done so, connect the sending unit first and then apply the power...if the needle still pegs out you have a short in the wire...and you could rewire the sending unit (using the same gauge wire) externally to the gauge...and you should get proper readings...unless the sending unit is fried...in which case applying power would give you an empty level...infinite resistance..
That would require replacing the sending unit...not sure if you can get the parts directly...if not then finding a sending unit from another 24 volt application would be needed...
But that could be normal...with power and ground without any resistance as is built into the sending unit it would peg out...like hooking a volt meter to 110 service with it set at 10 volts...
The gas gauge works as a potentiometer and provides resistance according to the level of gas...
If you haven't already done so, connect the sending unit first and then apply the power...if the needle still pegs out you have a short in the wire...and you could rewire the sending unit (using the same gauge wire) externally to the gauge...and you should get proper readings...unless the sending unit is fried...in which case applying power would give you an empty level...infinite resistance..
That would require replacing the sending unit...not sure if you can get the parts directly...if not then finding a sending unit from another 24 volt application would be needed...
You're absolutely right. I hooked everything up and the needle still pegged out to full so i used the end of the sending unit wire and touched it to ground and the needle went to empty. So i bent the end of the wire closer together and hooked it back up to the sending unit and now it seems to be working correctly. I guess it just had a loose connection at the sending unit. That's pretty weird that it pegs out to fuel with a bad connection.
Mark_88
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Good to hear it was something simple...can't imagine who you would go to for a wiring diagram on a military vehicle...it's probably classified and you'd have to use Access to Information...which is probably harder than using a fishing line like electricians do to pull wires...
Its not classified. If you want manuals for military vehicles google "logsa etm" when you get to a search page with 5 or 6 search fields, type the vehicle nomenclature into the field labelled "pub text." wire schematics will be in a -20 or higher manual.
Mark_88
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