You are still not listening to what I'm saying. Good day.

 

Well, if it is anything like the old school ones I used to work on for school bus (BTW, you know those stop arms with the two strobes on it that alternate? Yep, I helped with R&D on those back in the 80's), they measure current, and if the circuit wasn't completed, then the light on the display would also be out. It had a display that looked like the back of the bus with the red and yellow lights on top as well as the brake and turn signals. When a light was lit outside, the corresponding light on the display would also light up. It used reed switches and coils.

Today electronically it is doing something similar, but more advanced as it can tell if a bulb is out, missing, or has bad wiring, without first lighting up the lamps. When I picked up a new flatbed trailer, one light wasn't fully inserted, and as soon as I started the truck warnings popped up, and the trailer wasn't even set up yet in the truck. So it is using continuity to check, which means it is looking for a low resistance in the circuit.

 

I think many are missing a point. If detecting a specific trailer was a feature, it would also need to tell the difference between my 16' enclosed and my 20' enclosed. How do you engineer types intend to handle that? Saying the truck should have a feature and presenting the simplest scenario only (4 pin no brake vs 7 pin with brake) is misguided.

 

Apparently, some people can't comprehend that. Maybe even some electrical engineers.