2001 W-900B headlight issue

Also pull your fuse panel back and look for corrosion on the back side. The windshield may have a leak.

 

My truck is older. Washernut on the dash switch was loose, controls ground apparently.

 

Another possible cause is the flex wiring below the hood hinge/s, any place wires flex repeatedly is a likely place for the wiring to crack/break inside the insulation, while having the outward appearance of being in good condition.

 

Can you hear a circuit breaker cycling when the lights go out? Due to safety regulations, headlights are supposed to be on an auto-reset style circuit breaker rather than a fuse. I have sometimes seen them trip simply because they started getting weak over time. That and the fact that if you like keeping the cab heat aimed at the floor, it can warm up the fuse box and that little extra heat can cause a weak breaker to trip. Either that or you have a ground fault (ie wire rubbed on the frame somewhere). If the breaker is cycling, be sure to replace it as they get weaker each time they cycle on/off.

 

I could hear the breaker on my 94 and we found a place in the wiring coming from the turn signal grounding on the frame of the steering column. I finally had to disconnect the low beams and reaim the high beams just to get home.

 

I just started having the same issue on my 00' W900L tonight. It happened once while I was parked at the truck stop messing with it. I switched relays with another one but that didn't help.

 

check ground from headlight bucket to side of radiator/CAC, there is one on each side. if that's not it make sure all the dash grounds are clean and tight.