The vent/drain unit is wrong for your truck. The '01/'02 drain/vent is yellow and has a hole for the grommet to run trailer wiring out in that location.Yeah, my guess is that the rear quarter panel was replaced with one that was not configured for trailer wiring. I expect the white/gray coupling should be outside/under the body. I don't know where that grommet should go, but there's no hole I can find.
The vent/drain unit is wrong for your truck. The '01/'02 drain/vent is yellow and has a hole for the grommet to run trailer wiring out in that location.