Yes, PDC is the power distribution center.
BCM is the Body Control Module. Controls lots of the functions that reside as systems in the body of the vehicle. As in this case, the BCM controls the external lights. When lighting is requested, either through the manual on selection of the switch, or the automatic light sensor system, the BCM controls voltage to the various circuits to turn on the lights. Also in this case the clearance lights get their voltage via a relay in the PDC which is hot on one side all the time, but the relay is open until the BCM receives the signal to turn on the lights. At which time it provides a ground to the coil of the relay, the relay closes and voltage is supplied to the light circuit.
if the relay is stuck closed, the lights are on always. If there is a ground on the relay coil when there’s not supposed to be, the lights will be on. If you remove the ground and the lights go off, the relay is ok and you need to find why the ground is there when it’s not supposed to be.
The BCM is located behind the kick panel at the left end of the dash on my 2020.
What year is your truck?
