Troubleshooting an issue with a 84 Pickup - 22R - 2WD. It sat for a number of years somewhere in OK until I bought it, overall it has been stable and recently did a 1000 mile trip without too much hassle.


One issue that came with the truck is the fuel gauge is stuck at below empty, and after running the tank down to various levels I have never seen it respond. The temperature gauge works fine.


I am currently approaching the issue from a few different directions:

1. Sender float stuck to bottom of tank
   1. Car sat for an extended amount of time
      
   2. Fuel filter was full of brown nastiness before I replaced it
      
   3. Probably not just a gunk on sender problem as it does not respond at any fuel level
      
2. Ground/Electrical issue
   1. This appears to be a common issue where the wires on top of the sender unit corrode or get disconnected
      

So far the actions I have taken with regard to the issues laid out above:

1. Sender/Tank issue
   1. Adding seafoam, has only been about a week but so far no change
      
2. Ground/Electrical
   1. Checked condition of wires at the top of the sender unit
      
   2. Checked condition of plug between sender unit and bus
      
   3. Checked voltage across the gauge at the dash panel - read ~4.0V
      

Where do I go from here? I'd like to exhaust my options before I go to taking off the fuel tank.



Bonus Question: When I was following the wires back to the engine I found this unplugged near the radiator, it looks like a trailer light plug, but I'm not sure.

 

I have a feeling you're going to have to drop the tank, and remove the sender unit to replace it. Given what you found in the filter, it's probably going to necessary anyway, to clean the crud out of the tank. I would bet there's a ton still left in it. You will probably need to get the tank chemically stripped, and then sealed up.
So yes, if I had to guess, sending unit got all gunked up. It may be repairable, but I wouldn't bet on it.

That mystery plug does look like a trailer plug. Like if someone had been towing the truck behind an RV, or something like that. Might be wrong, though.

Good luck!
Pat☺