Headlights not working grounding issue?
 

I'm running into and interesting issue with the xj headlights

I installed the K suspension headlight wiring harness with the rampage housings almost 2 years ago and there have been no issues.
https://www.ksuspensionfab.com/store...t_Harness.html

last night the headlights would not turn on.

Here's what I've diagnosed so far:
Relays are activating, replacing/swapping relays did not help
Ground connections test good with the volt meter. (Could still possibly be an issue)
At the h4 harness without the headlights plugged in I read 12 volts when headlights are turned on and 12 volts when high beams are turned on.
Headlights work when I wire straight to battery (so bulbs and housing are good)

The moment I plug in one of the headlights back into the h4 harness I get 0 volts on the other side harness. Doesn't matter which side or which headlight is plugged in.

Any ideas?
Thanks everyone

Took a deeper look last night.

Turns out the inline fuse to the relays was a little crusty which wouldn't let the required voltage through when the relays call for it.
Cleaned up the fuse, applied dielectric grease, all works as expected.