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Classic Truck Discussion Forum

Ford f100 1970 truck gas guage

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05-14-2015 19:01:06

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Guage does not work. On this model gas tank is in the cab. Easy to see sending unit behind seat. How do I test it out to see if it is sending unit OR the gauge on the dash.

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08-31-2015 08:20:26

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 Re: Ford f100 1970 truck gas guage in reply to Jo Bird, 05-14-2015 19:01:06  
Its really simple on these old fords. All you need is a 12 volt test light. If your temp gauge is out also then your IPVR is probably bad, skip to check "c"

1) All test made with KEY ON... test the sender wire at the tank. You should get a dim pulsating light. a) if you get a dim pulsating light then the circuit and the gauge are GOOD.
Sending unit is bad or tank?unit is not grounded.
Run an extra grnd. to sender and retest.
If extra ground does not fix it then remove unit, check float and arm, make sure float is NOT FULL OF GAS. hook up wire and ground unit. moving float arm should make gauge move. If it does NOT. replace sender unit.
b) If you do not get a pulsating light at the tank then check the terminals at back of gauge. You should get a pulsating light at BOTH terminals.
If you get a puls. light at both terminals then wire to the tank is broken.
If you get a pulsating lift at ONE terminal then the gauge is bad.
If you get NO light then the Instrument panel voltage regulator is bad OR not getting power.
c)Locate and test regulator. ( rectangular box on back of instrument cluster) It should have 12 volts CONSTANT power on one terminal and a puls. light on the other. Constant power on one terminal and no power on the other means the reg is BAD....No power at all means the power source is open..
NEVER GROUND ANY WIRE on the gauge circuit as this could burn up a GOOD gauge.....

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08-26-2015 15:22:46

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 Re: Ford f100 1970 truck gas guage in reply to Greenfrog, 05-14-2015 19:01:06  

Just found your post, haven"t had to fix my "67 but the "67 through "72 are mostly the same, so here are the wiring diagrams. The wire from the sender to the gauge is orange, the other wire from gauge is green/black. I"ll keep an eye on this thread if you need more.

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05-14-2015 21:46:43

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 Re: Ford f100 1970 truck gas guage in reply to Greenfrog, 05-14-2015 19:01:06  
One of the first things is to make sure that all wiring connections are tight and properly grounded. Other than that, I cannot properly explain the procedure here. Check YouTube for videos on fuel gauge problems.

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