My 86 K5 fuel gauge does not show full, it will only show 1/2 tank when full, any idea what is wrong. I'm not the best when it comes to electrical work. Would like to take it on a long trip with out stoping every 2 hours for fuel.
Thanks in advance for any help.

Art :fb:

Could be the float ball in your tank has a crack in it and it is shipping fuel and sinking inside the tank. Try to fill it up and see how many gallons it takes. Write your mileage down on a log. Figure that against your known MPG.
If the float ball is sunk, it's an easy fix. If it's the resistor on the float level arm, a new unit will cost you more than the brass float ball. Check your wiring to make sure that' s all good. If it's in a Blazer you will have to drop the belly tank to check on the fuel level sender and it's float ball. Not sure about the '86 vintage.

You can easily find out if it is the gauge or the sending unit in the tank by grounding, what I believe will be, a "tan" wire going to the gas tank. If the key is in the "ON" position the gauge should go all the way to the full mark. If it does not, the gauge is bad. If it does, the sending unit is bad or wire connection could be bad. Make sure the wires are not burned by dual exhaust pipes, and even that the tank is grounded. If the tank is not grounded properly the truck cannot circulate current through the sender properly.