2000 XJ Sport.
Sylvania Silvertar Blubs 55w
Daniel Stern Headlight wiring harness

I recently have encountered a situation about which I need help in trouble-shooting the problem. Some years ago I installed the H4 lenses and bulbs. No problems whatsoever for years. Recently the only headlights I had was when on brights. I checked fuses, headlight bulbs, & connections including the relays. Changing the position of the relays made no difference. When I connected the bulbs to the original headlight harness there were no issues, I had dim and bright lights. I replaced both relays (Hella Relay 40amp), cleaned the relay sockets and the headlights worked normally, switched from dim to bright without problem. Unfortunately this only lasted for about three weeks and the headlights are only on if on the bright setting again I again bypassed the harness and the lights work fine. I am uncertain what to look for that would be causing a relay to fail. The light sockets on the harness look fine and I see no evidence of any kind of arcing. The relay sockets also visually look fine.
Not sure where to look next. I guess its possible that I bought a bad relay but does not seem likely. Thanks for any advice.

 

Sounds like you know a lot more about this stuff than I do - but I'll share that when we had problem with our h4 lamps it turned out that the harness was no longer properly grounded.

 

Does your newer harness connect to the old headlight connector on the passenger side like most setups? You could try making an extension to the drivers side and use that old connector as the new relay trigger...at least worth a test!

 

You might check the current coming off the dimmer switch. A pain I know. Had this problem on another car and a worn dimmer switch was the culprit. It does interrupt the dim light current when on bright.

 

Unless a component has melted or is currently in flames purely visual electrical inspection is fruitless. Obtain a DMM and wiring diagram if necessary and start tracing the circuit to test where the voltage stops, that will at least give you a start. If you've never used a DMM and are unfamiliar with basic 12V electrical theory there are plenty of YouTube videos to guide you.