I'll kindly disagree with your statement that it worked before, as kicking codes and flashing dash lights are enough justification that it didn't work properly.
As for the lights not illuminating; when the car is on with no trailer there are no lights on the trailer brake controller whatsoever...
Dealer added a wire and now it works, however it doesn't light up.
They said they hooked it up to a trailer tester and it worked. They didn't mention it doesn't light up.
For sure something Jeep dropped the ball on..
I've noticed it a bit, and stumbled across heated wiper blades. More curious if they work than anything..
Doesn't help I did tint the window - logic tells me that if it keeps heat out, it will keep heat in.
However, I shall check back in... When it snows again :)