Hello all! I know this topic has been talked about to death, but never heard of what my gauge is doing. Anyway truck is a 89 that was a R3500 converted to 4x4, also was a fuel injected 454 that I converted back to carburetor with a different 454. Fuel tanks are still the TBI tanks with baffles for the fuel pump. Over a year now I have always just topped the tank off when I get to 1/2 since the gauge will not go under a half a tank. Gauge is accurate showing right at the full mark when tank is full, 3/4 tank shows 3/4. Get to 1/2 it's half. Needle goes just below the 1/2 mark and there is stops. Some weird reason today I was around 1/2 tank and was running on rough terrain and I see it go into uncharted territory. It was closer to 1/4. Ok, maybe the float is getting stuck on the baffle? I switched out the original sending unit that had the fuel pump attached to it and swapped in an carbureted engine sending unit a year ago when I built the truck. So I thought maybe the two units are different. I shut the truck off, and came back to fire up and leave, the gauge moved back to its usual spot of just slightly under half. Ok that theroy didn't hold up I guess. Ok details. I changed out the original large gauge to put in an tach. So I bought the small fuel gauge for the lower left spot. Think it was for the 79-81 model years. Thought I seen those run same ohms as the later years, 0-90. So I ended up doing a hard wiring conversion to bypass the original circuit board that ran the large fuel gauge. Grounded to the ground bus on the left side under dash, ran 12 volt to accesory terminal. And spliced into the sender wire, pink/black strip on my 89. Seems to work above 1/2 tank so I figured my wiring was ok. I've moved the sending unit ground to the frame, it's good and clean and bare metal, show ground there should be good. Tests. I have conducted the ground loss and sending wire loss test. Disconnect ground, gauge will go to "E". Disconnect sending wire, needle goes to 3 o'clock. The gauge did not come with a resister in back of it. Just a plastic look-a-like resister. My original gauge is long gone and didn't realize I may of needed that. Sorry for making this really long. Just really have no idea what to check next. Suppose next would be move bed off and pull sending unit and check its ohms. Any ideas guys? Stuff was from an aftermarket company that I guess can't be posted here, starts with L as first initial.
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