Originally Posted by Bucko

A simple test light (or better, a multimeter) will provide you with the answer. With the headlight switch in the headlight position, you will have 12 volts to energize the headlight relay. From the output of the relay, you will have 12 volts to the headlights.

Start at the heatlight wiring socket. With the headlight switch on, prode for 12 volts, working your way back to the relay, fuse, and headlight switch.

It's very rare for a headlight switch to fail; no high current flows through the switch. It's mearly a trigger switch for the headlight relay. This relay is what provides the 12 volts and current to the headlights themselves. I'd suspect it way before the dash switch.

Unless you were tampering with it....

Originally Posted by xtremestang

Hi I just pu a 03 HD and the when I first start truck one HID headlight works until I shut light switch off then back on ..... then both HIDs lite up. Would relay cause this problem!!! Same goes when I use auto start .... Ihave to turn switch counter cw then cw.