I have a 2003 Chevy Avalanche and the passenger side brake light and running light just stopped working I unplugged the pig tail from the box under the rear fender and cleaned it out and plugged it back in so I went and bought another pig tail and plugged it in still nothing but now only the turn signal work's and the hazard work's (I'm guessing cause it uses the same bulb) but all the bulbs are good cause I inter-changed them with the driver side just to make sure the bulbs were good all fuses are new and none are blown... could that one plug be bad for that side in the box under the rear fender... please help... I've done used my fix-it-ticket up and already got an $115 dollar fine for not having it fixed

You'll need to trace both power and ground for the portion that isn't working.
Is this something that just suddenly happened? Sometimes corrosion can build over time and cause these symptoms.

Yes this happened all of a sudden... one day all was good and I guessing a couple days later is when I was told while pulling into a gas station I had no lights at all on the passenger side, ive even cleaned the corrosion off the terminals and sprayed with anti corrosion but still no brake light or driving light, just turn signal and hazards when used....

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Originally Posted by CaptainRich

You'll need to trace both power and ground for the portion that isn't working.
Is this something that just suddenly happened? Sometimes corrosion can build over time and cause these symptoms.

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Yes all of a sudden just stopped working all was good and I think a couple of days later I was told while pulling into a gas station that all my light were out on the passenger side... I unplugged the pig tail from box under rear fender and clean all dirt and mud and even sprayed anti-corrosion and still nothing... but the turn signal and hazards do work just no brake light or driving light for that side

Both the left and right brake lamps share the same feed through the junction block at the rear. If you've swapped the bulb, I'd take a closer look inside the suspected lamp socket. The tabs will brake off and look like they're still attached but aren't.
Use a powered test light to verify the ground tab is still intact.