Phillip:
1) You need an inline voltage drop to handle the 12 volt blast going to your 6 volt sender and guage.
2) Check your wiring against the
factory GMC wiring diagram. 3) Your truck was converted from 6 volt positive ground to 12 volt negative ground or 12 volt positive ground? This will also possibly affect the guage.
4) Cut a nice fresh curved branch off a forsythia bush and keep it behind the seat to stick the tank! (I'm kidding I'm kidding!)
5) Using that factory wiring diagram and a volt/ohm meter, you can trace your guage wiring to make sure you have the wires where they are supposed to be.
