M925A2 fuel gauge, parking brake light, low air light problem.

[SPIKE66]

OK guys, I'm new to the 5 ton and Steel soldiers. I have been trying to take in all the great info on the forums.
I just purchased my first 5 ton truck, 1990 m925a2. Drove it 7.5hrs from PA to Northfield OH and no problems. The truck ran great but having an issue with my fuel gauge. All my other gauges are working. No matter how much fuel is in the tank, It bobs around full or stays past full, drops down just a bit when the truck is not running with ignition on.
Also my parking brake light does not come on when the parking brake is on, I do get the tone when the parking brake is on.
Also my low air light does not come on. All the bulbs are good.
I'm decent at wrenching on vehicles and just looking for a trouble shooting start point.
Any pointers would be great.
Thanks.

 

[URSATDX]

My parking brake light and low air warning lamp were both ground issues.
I ran new ground wires and both work fine.
My fuel gauge has, only recently, started to act up.
I will check grounds at the sender and the gauge cluster.
If that does not work I will remove and clean the potentiometer on the sending unit.
Welcome to the game and good luck.

 

[simp5782]

Is there power to the bulb sockets with low air or the parking brake on?

Fuel gauges are notoriously unreliable. Ask 74m35a2. Ground the gauge to a better location and redo the ground from the tank to the frame is the best start

Never trust your fuel gauge even if it's got a new sender. Wires and gauge.

 

[SPIKE66]

Thanks for the info. Will start with ground and check power to the sockets.

 

[URSATDX]

I removed and cleaned the fuel sending unit. (Brake cleaner)
Works like new.
I 'd guess something was building up on the metal contacts.
Bought some Biorbor JF biocide as a PM additive.

 

[74M35A2]

Whenever I'm bored, I just let the 925a2 run out of fuel wherever it happens. Provides for an evening of entertainment.

Bothering friends, working by flashlight, explaining to police what happened and why I own such a silly piece of equipment, 2,000 numb thumb pumps of the primer, opening of bleeder screws, digging for my Jerry can nozzle and asking myself why I have not bought a new gasket for it yet, spraying 1/2 a can of ether under the intake mushroom cap, wondering why nothing ever comes out the bottom of the frame mounted canister bottom drain, excessive cranking until the fuel cut solenoid magically extends, thinking how much longer I'll have to work or until a doctor tells me I have cancer, and then the engine finally firing 3 seconds prior to the batteries submitting their resignation.

A total riot.

 

[74M35A2]

No ground at the gauge. System is simple. Voltage applied through the gauge, sender has the ground. That's it. Both of mine were bad, and that made it nearly impossible to diagnose until changed both at same time.