Yes u need a resistor in line for the gas guage if u are converting from 6v to 12v. My sending unit in the gAS tank was "blown" (wire on unit inside tank literally broke) probably due to running 12v w/out the resistor. The resistor will go between the ignition switch and guage. Do a search for correct resistor as it has been coverwed many times. Or I'm sure someone will chime in with right one. I'm just old and can't remember!!!!
