Electrical Problems in Rear Bumper

First I noticed that when the parking assist system is turned on, there is a message displayed on the infotainment system that says it should be serviced at the dealer. With some reluctance, I had the dealership perform an inspection and was told that they found a code for the wiring harness in the rear bumper with an open circuit. The parts and labor came with a pretty hefty price tag, ~$720.00.

I've since noticed that the lights that luminate the rear license plate are also not working.

My suspicion is that when the previous owner had some work done (aftermarket reverse lights installed into the bumper or tailgate pop lock) the wiring was inadvertently damaged or done incorrectly.

I've already visually inspected all the electrical connections in the rear bumper and wasn't able to find any obvious problems.

Just to note, the brake lights and reverse lights still operate correctly. I've only noticed problems with the parking sensors and the license plate lights.

My questions:
1) Does anyone have any experience in testing the electrical connections in the rear bumper that would be related to the sensors and license plate lights? Can you provide diagrams, instructions, tips, etc.
2) If I can't resolve this myself with a multimeter and some electrical tape, what would be the best way to find an expert on this subject? I'm assuming replacing the entire wiring harness is probably overkill.

 

Rear bumper harness, you’ll have to take the e bumper off and play with the harness and see what’s no good

 

Try this wiring diagram.

 

Thanks! This might come in handy at some point. Is there a centralized place for wiring diagrams like this?

 

@caribe makaira is the electrical guru here but I’ve attached the big file that I found here previously.

 

Seems you might have a big issue on connector BE2, since it handles the CanBus circuit and shares ground with license plate lamps.

 

If any electrical gurus in Los Angeles see this thread and know how to troubleshoot this, please PM me for some work.