Fuel Gauge Pegged to Full

stwilegar

stwilegar

Member
Just installed new gauges. The last to be terminated was the fuel gauge.

The pink/red wire is terminated to ground on the body. The black wire is terminated to the proper signal wire. This was the oposite of what I thought but according to the diagram.

The gauge is now pegged to FULL and I know the tank is only about 3/4.

My guess is I have a grounding problem. So, I ran a aligator clip wire and grounded it to no avail.

When i disconnected the battery, the gauge is still pegged at full. Not sure what to think about that.

Any ideas to make this gauge function properly would be appreciated.

TIA
Bridger
North Idaho
 
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This post caused me to have some questions right off the bat. Knowing you're fairly new to the forum, I rifled back through some of your earlier posts to glean some intel about what rig you're working on and whether these new gauges are stock replacements or after market etc. In doing so, I found the answers to some of my questions. I said all that just to illustrate that the backstory details and specifics of a given situation really matter when you start a new thread. '72 Scout. Isspro aftermarket gauges and an aftermarket wiring harness. Ok, so are there any factory wires remaining on your Scout, or is it 100 percent new wiring throughout? If it's all new, then I suggest you refer back to the wiring kit instructions, which I'm not privy to, and double check your work. If there's a blend of old and new wiring in certain areas, specifically with regards to instrument and associated sender circuitry, that would be vital information to include at the outset. So please clarify if you can exactly what you have going on here wiring wise between the sender and the gauge.
 
Hey Scoutboy. Thanks for taking the time to gather intel. Yes, I am building a 72 with a 345 and auto xmsn. Thus far, I have installed an American Autowire harness bumper to bumper with Isspro gauges mounted in a new gauge face.

The entire rig is 99% new wiring. There are very few wires existing from the original. However, the wires from the fuel tank sensor are original.

I followed the instructions meticulously and found that all the other gauges function as they should.

The wiring for this unit is new from the gauge to the rear. During the rewire, I cut these wires from the fuel tank which was installed by the previous owner. So, I've utilized what look to be the original wires from the sensor on the tank to brand new wiring to the gauge. The ground wire is grounded to the body in the rear of the rig.

Interestingly, when I tested the guage wires to be sure I was using the right ones, the gauge seemd to function properly. It showed 3/4 tank and cycled on and off with the key. When I made the connections permanant, the gauge pegged at full and never returned even after the key was in the off position and positive battery terminal disconected. Following this series of discoveries, I even disconected the ground wire to no avail. My fear is that I inadvertently smoke the gauge itself?

Aside from this, how would you go about diagnosing this challenge?

Thanks in advance.

Bridger
 
Thanks for the additional explanation. According to the diagram in the IH factory service manual, the fuel gauge sender pigtail wires were 18 gauge Red and Brown. Age and element exposure may have discolored them slightly. In reality, the coloring of the wires is less important than how each of them was physically terminated at the sender itself. In original configuration, the Brown wire received chassis ground and terminated at one of the sender flange fastener screws, while the Red wire was for sender to gauge connectivity and terminated at the center post of the sender itself. Unless I'm misreading your initial remarks, this would appear to be the opposite of how you made your final connections. I share your concern regarding the inability of the gauge to reset with power removed. Unfortunately, I would likewise conclude that the gauge has failed.
 
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Indeed, I believe you are correct. Not sure where I read it but at the time the wiring made no sense. I reversed the wiring and that seemed to do the trick. Fortunately, nothing seems to have been permanently ruined.

Thanks very much for ykur expert assistance.

Bridger
North Idaho
 
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