I have had the HD dual lamp assembly on my FLHX since 2006, and until this week it has functioned without any issues. Now my low beam will not light when the switch is in low beam, but when high beam is switched on, both lamps light. I bench tested it with a 12v battery, and discovered it is in the little box in the wiring harness that has a high beam white wire, low beam yellow wire and a third wire that goes out to the low beam lamp (I believe this is like a diode allowing power to flow from the high beam circuit, but when low beam only is selected it does not allow power back to flow to the high beam). So, I see HD sells a new harness for $80 to replace the whole lamp harness. I think that is a ridiculous price. I am handy, and I am thinking a simple diode or switch can be added to this without buying a new harness.

Does anyone have any ideas for a fix?