Headlight problems

[Sh75]

So my truck has the four headlight, however the dims have the top two lights on like normal, but when you turn on the brights only the bottom right light is on. My dad seems to think it's the dimmer switch but I just replaced it a little under a year ago, does anyone else have input?

[rich weyand]

It's not the dimmer switch. It's the wiring under the hood behind the headlights, plus maybe the wrong bulbs.

This is the 1986 quad headlight circuit diagram. Probably the same.



Note that the hot goes to the left (drivers) side first. If the passenger side is the only one lighting, then it sounds like a bad ground splice. Note also that the uppers (marked HIGH AND LOW BEAM) should be on as well on the other filament, so either the hot is broken to the upper high beams (LT GRN wire), or someone put the wrong bulbs in there.