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I just purchased this truck 3 weeks ago and I'm in the process of learning what makes it tick. This truck is a blast to drive.
The truck has had a new fuel tank put in by the previous owner.
I need to know what I should look for first. All of the other gauges work and the rest of the electrical system components function properly.

Thanks,
John

Fuel tank may be new, but is the fuel sending unit? Or, the gauge itself may be bad. Not being a mechanic myself my line of thinking in this regard always hinges on replace! start with the sending unit. If that doesn't work, then the gauge.....At least thats what I'd do.

I would like to narrow down the problem prior to buying parts.
Is there a way to test the sending unit with an ohm meter? What kind of values would I look for?

Hello Highway Man,
I'd start by attaching a ground wire to your fuel tank. My gas gauge didn't work right either, even with a new gauge and sending unit. Once I added the ground "tank to frame" it has worked perfectly. Also, I can post the troubleshooting info tomorrow if you'd like.
Gary

The info provided with this link should help with testing the gauge and sending unit.

http://www.cj3a.info/sibling/milgauge/milgage.htm

Carter,
Thanks for posting that link. I will check this out in the next couple of days.

Gary,
I tried grounding and it made no difference. This was actually my first thought since the tank had been R & R.

Thanks Carter for posting what I was going to have to manually key in!
Gary

You are both welcome, I have that site book marked so I can find it when ever it's needed. I have to check and see if the senders and gauges work on my red 52 M and may need it myself soon as Ralph and I bring it here to my shop which should be in the next couple of weeks if all goes as planned.

Just for the record, is your truck 12 or 24 volt?
the gage does not work on 12 volt.
Rich

poor rich wrote:Just for the record, is your truck 12 or 24 volt?
the gage does not work on 12 volt.
Rich

My truck is 24 volt. The electrical system is unmolested except for the horn wiring. Everything else on the truck functions as it was intended.

An inmolested M37? You truly have a rare one indeed!
Gary

T. Highway wrote:My truck is 24 volt. The electrical system is unmolested except for the horn wiring. Everything else on the truck functions as it was intended.

Have you replaced your wiring harness? If it is "original" than the insulation on your wires is most likely dried out & cracked. If the sender wire is shorting out along the frame, then your gauge wouldn't work (and you're setting yourself up for a fire). Check first for continuity between the gauge end and the sender end (no resistance). If that's ok, then check the insulation on the whole length.

The wiring seems to be original. I have checked the wires running back to the tank and they are good.
The only fraying that I see is in the engine compartment and has had electrical tape applied to it so that I can drive it until winter when I plan on restoring the truck. I will do an off the frame restore and a new complete harness at that point in time.
I took an airhose and removed some of the undercoating in the wheel wells / frame and found Strata blue paint that still has a shine to it.

Cool! An Air Force truck! It's gonna be blue when you get it all restored, isn't it???

Lifer wrote:Cool! An Air Force truck! It's gonna be blue when you get it all restored, isn't it???

No Blue here...........Green all the way