My dimmer switch dims my tail lights?

[krmill23]

So I made sure I had good grounds and grounded the body to the frame in 4 spots. I found a bunch of melted wires coming from the alternator and running along the front of the truck to the battery and replaced those. The brake lights weren't working but that was just a blown fuse, now they work. But still the dimmer switch controls the tail light dimness, one brighter than the other, and when the headlamp switch is pulled out, the left tail light is so bright there is no difference when I hit the brake.

I'm running out of ideas! Is it possible that this is the headlamp switch? I have the instrument cluster out it would be pretty easy to replace. Thanks for your input!