Pulling my hair out, what little I have
 

My wife's JKU is having a headlight issue... These are aftermarket LED headlights, don't know the brand. When she turns on low beams, both shine fine. She turns on high beams and the passenger light goes ouy completely... I have swapped the left with the right, issue stays on passenger side. I have pulled apart all connectors and put dielectric grease in the fittings, no luck. I have made sure all connections are properly seated, no luck. Last night I did several things and had them working fine laying on her bumper, re installed them, they still worked great.. This morning, she texts me when she's leaving for work saying they were working great. After work, she gets in and passenger light is out again.. I don't know what to try next.. Last night, I did find that headlight adapter plug not seated properly, was about an 8th of an inch from full seat... What should I look at next???

That sounds like a smashed up wiring harness somewhere. The intermittent function is a big split wire flag for me. I usually get it behind the passenger headlight where the harness is routed by the suspension. I've had two issues there though mine were definitely from changing steering parts and getting contact during flex. Both times I had a handful of wires to repair which were giving me shorts or breaks. I'd check the headlight harness from the light back to the TIPM, and I believe you can check continuity from the TIPM harness to the headlight connector.

The harness is pretty well protected out of the factory though. I had headlight issues and I'm sad to say that they were all self-inflicted. I had cut and spliced my harness years ago and the corrosion finally caught up with me. I ended up having to cut and re-splice the harness to undo my earlier mistake. Since fixing that, I've been trouble free. Maybe your previous owner did some wiring modification?