The most common cause of no/intermittent headlight operation is the dimmer switch. It lives in a very hostile environment behind the driver's side tire, catching all sorts of mud/water/salt splash. Check the switch and the connections going to it before you start shotgunning expensive stuff like a new harness at a simple problem.

I like to wire headlights through a couple of relays, and only use a (new) dimmer switch to carry the very low current flow to trigger the relays. You'll be amazed at how much brighter the headlights can be, particularly if they're running on 6 volts.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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