Dim Headlights on 05 379

I had a problem like that and the plug at the hood was loose and was jumping the current around and the dash lights would come on and stuff. Electrical problems are the worst until you find them and are usually the easiest to fix. Good luck

 

The headlight circuit is a little funny on big trucks. Poor grounds or open circuits will make you scratch your head.

Many times it's the ground is corroded at the chassis. I have ran new grounds to both lights as one ground runs across the lights then to the chassis. The chassis bolt will hide corrosion under it. Looking at it you might think it is okay until you take it off. You should have clean metal under it.

Since he replaced the headlights he probably used butt connectors. They can very easily trap road salt and moisture and corrode out. Check each one closely. If he did use the standard butt connector I would go to an auto parts store like Advance and buy the waterproof butt connectors. It is nothing but a butt connector inside heat shrink. You can use a BIC lighter on one and that would stop any corrosion problems in the worst weather. Cut back to clean wire if you do that.

I don't think the problems lie in your relays or you would have lights going out instead of dimming. You can borrow relays from other circuits for a short term test. There should be a diagram on the side of the relay. Just sure they are similar. The typical headlight relay pin 30 goes to the lights, pin 85 goes to ground which I suspect, pin 86 goes to the dimmer switch and pin 87 goes to battery +.

This is a resistance issue due to a poor connection somewhere and probably within 2 feet of either headlight.

 

Yes its a pain but alas u do--on my 05 we had to rewire recepticals for 2 of the relays due to moisture--didn't bother connecting back to panel but just left new relays and wiring hang off to side
Good luck