[firebear]

you can disconnect it and try each lead by its self to better determine if its your trucks wires or if its the bar try reversing the left and right and see if it still does it (left hooked to the right//right hooked to the left) if it still does then i would bet its in the bar may be a simple grounding issue or might be somthing alittle more involved the requires it to be returned hope that helps
also if its in a seperate circuit it shouldnt have to have a resistor since the light bar is self contained