My headlights will not turn on, but my tail lights and park lights will though. I have replaced the bulbs so I know that it is not them. They were working when I went into the store and when I came out, they wouldn't turn on.

 

Any fuses blown? What all have you checked? I had a car that would do that, but it was with the tail lights instead of the headlights. Turned out to be a bad ground wire. Check to see if you have any ground wires running from your headlights and also give your wiring under the dash a thorough look over as you may be able to find something. It also helps to have someone toggle the switch back and forth as your looking at wiring, you may see a spark that will tell you where your problem lies.

 

I have checked the fuses. As I was messing with the dimmer switch, I noticed the the lights would turn on for a brief second and then back off. But it only did this when I was going to low beams. Could it be the dimmer switch then?

 

yes. what year is the truck?

 

Yes it's the dimmer.

 

87 4.9l