Try to replace the headlight pig tails the may be bad had the same problem drove me nuts try napa only place I found them

 

i hd the exact same problem with my Chev, turned out to be the headlight switch. In the on mode it wasn't providing power to the low beams, but when I put on the high beams via the switch, they came on. Replaced the headlight switch and problem was fixed.

 

I am finished putting the truck back together after paint so now it's time to fix the rest of the minor bugs. I posted that my high beam lights work but as most of you know when you pull back the lever they automatically come on. Of course when you release the lever they go out. I needed a new key switch so while I was replacing it I replaced the dimmer/multi-function switch and the ignition switch. This didn't do anythimg to help. I can't find a seperate relay for the headlights. Does a 1991 have one? I am going to check the fuse links and the actual headlight swich for power> I switched the headlight swicth with a good one from another truck so I know that is not the problem. I am guessing a wiring issue? Does anyone have any suggestion? Thanks!

 

is there a black connector under the dash with a red and purple wire that is not connected to anything? if you can find it you should test for power at the purple wire with the low beams on. i think it should have power. the connector should be for plow lights.

 

I have a 1984 d150. The headlights, tail lights, and brake lights went out. I changed the fuses. No luck. The brake lights are getting power but not working. Turn signals and hazards are working. Any ideas?

 

are you sure the brake lights are not working? if turn signals and hazards are working so should brake lights. did you check the brake light fuse? it is different than the turn signal fuse. i would recommend looking at the fusible links under the hood. i think your looking for the red wire attached to the grey fusible link.

 

Did you ever find the issue? Currently having the same one.

 

Did you happen to look at the dates these where posted? Thread started in 2012 and the last post was 5 years ago. Make a new thread with your issue and vehicle details.

 

BLown fuse, bad ground, H/L switch, and high-beam switch have been my culprits over the years. Prove things out so you're not just buying random parts. Good luck.