Backup lights coming on when brakes pressed

We have a 2002 Malibu with 216,000 miles. Car in excellent condition and always garage kept. We have used the same mechanic for many years until this year when he closed his shop. We do plan to replace the car next year, but it's just not necessary to do so just yet.

A couple of month ago someone rear ended me and the body shop replaced the trunk weather stripping, rear bumper, light assemblies, repainted the trunk/bumper/rear side panels.

Several weeks ago, while hubby was pulling the car out of the garage I noticed every time the brake is pressed the backup lights come on too. I then checked turn signals, all other lights, etc. Everything else appears normal except this oddity.

I took it back to the body shop and told them what was happening and said it had to be something done during the repair work. He checked and said everything was hooked up correctly and I needed to take it to a mechanic because it wasn't anything they did.

I have researched and researched and found several other people with this problem. One answer was that the new light assembly was after market and the "pins" were not compatible with the original wiring harness. Another was that the wiring harness coming from the trunk was somehow damaged.

What do others think before I do take it to a mechanic and spend money I should not have to spend?

Most likely a pinched harness from the accident. Or possibly poor rewiring in repairs.

Key on, engine off, e-brake applied car in neutral...hit brake pedal....brake lights and backup lights on?

Now take your foot off the brake pedal, lights should be out......

Now shift into reverse.....the reverse lights are on, but are the brake lights also on?