Hey guys,
I just bought a 86 K5, and I am having an issue with the fuel gauge. It tends to jump around, never giving me an accurate reading. Suggestions?

 

if its jumping around when driving I would say the baffle is missing in the tank
Otherwise bad connections on the sending unit or sending unit itself

 

another thing you can try is the k5 is pretty roomy underneath try following the wires coming from the tank along the inside of the driveside frame rail. i actually had one that had connection in the middle of it that was very corroded. i just cut the section out. i believe the fuel gauge wire is a pink wire, if you look at the wires coming out of the fuse box you should see it come out of the fuel box then go back towards the back of the truck, follow that wire