When my headlights are on low they are so dim you cant see at night and when on bright only the driver side works. Tried replacing bulbs and didnt fix the issue. Previously everything worked but the passenger side was dim on bright. Then one day it changed to what it's doing now. And it has went back to everything working twice. I dont know what I need to fix. Do you think they need to be completely rewired?

 

Bad grounds.

 

It does not need to be completely rewired, you need to figure out where the problem is. To begin with, there are no grounds at the headlights so "bad grounds" does not help, the way the headlights are wired is that they receive constant power from the battery via fuses in the PDC and the switches (headlight switch and beam select in the multifunction switch) connect either the high or low beam filaments to ground. That ground is inside the cabin under the dash so not in a location that typically rots away. You should still check it but if it was loose/bad there would be other things not working (e.g. the instrument cluster lighting uses the same ground G201).
Starting at the headlights, are these the correct bulbs ? A regular truck uses 9004 while the sport uses 9007. They might look the same at first glance but the pinout is different. Don't know how comfortable you are working around electrical circuits but as described above the switch gear merely connects to ground, so the way to troubleshoot would be to jump the violet/white to ground for low beam, the red/orange for high beam. Do that near the head lamps and if it the lights still act up the problem is on the power supply side.

 

You could attach a wire from the negative side of the harness near the plug for the headlights and run the other end direct to the battery negative terminal. Checking the voltage to the headlights would good also.

 

That was happening to me too. i got new headlights and purchased the headlight relay kit from LMC. It fixed my issue. If you have wiring issues at the headlight there is a good chance these two upgrades will help with that.

By the way there are grounds at the headlight, which can be tested, otherwise the circuit wont be complete. So the statement "bad grounds" is very valid.

 

Please provide pictures or references in the wiring diagram to support your statement.

 

If he has the sport headlights, the ground is on the left fender side shield. Wiring diagram on page 8W-50-5. Ground 102.

 

Fair enough, but like the other ground I mentioned in my previous response this one is not specific to the headlights, rather it's a shared ground coming from the PDC. The OP likely has not much experience troubleshooting wiring and telling him "bad grounds" can send him on a wild goose chase looking for a direct ground connection at the headlights which these trucks don't have. The ground connection is done through the switches (and relay in case of sport).

OP: Is this a regular truck or sport model ? OEM or aftermarket headlights ?

 

Yeah, the other one is inside the cab, center of the dash somewhere.