Was doing a How-To to installing aftermarket lights and this happened. I installed the lights a while back and they have been working ever since but here is what happened, and I'll try to be as detailed as possible. Came to the apartment had all four light bulbs working (it's a sport headlight so 2 bulbs on each headlight). Came out an hour later had no lows and only passenger side high. Now on my way to the apartment I had to hold the multifunctional switch for a few seconds for the highs to stay on and then it worked like it should. So here is what I did. I ran a power wire and ground from the better the the headlight (female) socket both highs and lows light up on both sides. Now I rested but the power wires and grounds on the factory harness side and both read good (used a test light that can rest both grounds and power) and they still don't light up except the passenger side high. What could it be? I'm thinking either the multifunctional switch or the headlight switch.

 

I even have the fsm but it didn't really specify how to test each switch

 

Guessin' these are LEDs. With the current info given...They are usually relay driven with some sort of external power supply for each light separately. Check to see if the power supply's work if you swap them one with the other, if the problem follows the power supply...problem solved, if not, recheck those electrical connections, especially the ground connections. Are you sure that you have a good/reliable ground. Proper grounding is everything in a modern vehicle. LED lights are no exception.

 

WHOOPS guess I should proof text before I post...if 1 power supply, check the connectors n wiring. May have been pinched or chaffed when routing during installation.

 

The lows are his highs are regular halogen. I do have a good ground. I am at a loss here

 

Then I would try doing a continuity check from the headlight switch down. I know these headlight switches can and do fail. You might also check to see if there are any relays between the headlight switch and the headlights in a wiring diagram.

 

No relays but I did add some a while back and they are good. I still think multifunctional switch

 

I will update if I find the fix

 

As of now I'm using a toggle switch and power wire from the better to all 4 headlights

 

Turned out to be the multifunctional switch inside contacts were corroded. So I took it apart and cleaned it.