Last night I was driving with my high beams on. Suddenly, both highbeam headlights quit working. I switched to the lowbeams and they still work. What is most likely causing this problem? Is there a relay that would cause this? Is the headlight switch bad? My truck is a 1994 F150 Extended Cab 4 x 4.

 

The very first thing you want to do is make certain that both bulbs are not burned out on the high beam side. One of the bulbs on the high beam side may have been burned out for a while and you just didn't notice it. There was a post on another site a while back where someone lost his dims and it turned out both bulbs were bad on the low beam side. Don't even think about doing anything else until you prove that this is not the case.

 

after that the next ting to check is the dimmer switch. Check for loose wires.

 

machawks

I'll go with a failed dimmer switch.

But check the simple things first.

 

When my dimmer switch went I lost both high and low beams.

I also went nuts checking everything under the sun before finally replacing the dimmer switch.

It's always the last thing you check that turns out to be the problem.

 

When mine went, I also just lost the high beams.

Every now and then they would come on for just a bit when you would switch to the high beams.

But that was just my experience.

 

Thank you everyone for your responses. As 88n94 suggested I checked the bulbs and sure enough they are both fried on the high beam side. I guess I was too narrow minded to think it could be the bulbs since they both seemed to go out at the same time. But, as you suggested maybe one of them was already out and I had not noticed. Anyway, I have replaced the bulbs and so far there have been no further problems. Thanks.

 

That proves the old theory of checking the simple things first.

 

I'm Having the same problem with my high beams, The headlight were the first thing I checked, they are good there is no power at the wire going into the back of both bulbs on only the highbeam side. A new $100 dimmer switch wasn't the problem either. I checked all the fuses under the hood and under the dash too, all good. Is there a relay that goes to just the highbeams? All the relays have the same part number, at least the ones that are the same size and plug configureation. I swapped them around and still no high beams. Anyone got any ideas that I haven't tried yet. Haven't striped the wiring harnesses apart to check for a broken wire yet, but just looking I don't see anything that looks like it could have cut any and see no signs of burnt wires.

 

I have a 99 F150 4X4. I also have lost my highbeams. I replaced the dimmer switch today with no results. I've also checked all the fuses and headlamps. All are good. I have no clue what the problem is. Is there a relay under the hood that controls the highbeams. The indecator comes on on the dash pannel. Lowbeams work but when you switch to highbeam they go out. Does anyone have a fix for this? It seems to be a common problem.