300SD ETR switch location

[cordesd]

My air conditioner in my 82 300SD stopped working all of a sudden, so I went after diagnosing the problem.

I have found that the problem lies between the a/c control and the compressor. I’m not getting a signal to the compressor to kick on. If I run a wire from the number 11 fuse to the compressor, it kicks on and cools wonderfully. I replaced the a/c relay, no luck. I tried swapping the electric temperature regulator on the passenger side kick panel with one out of my parts car, but no luck. I tore the dash apart to get to the a/c control and took it apart looking for burns on the circuit board but nothing. After looking at the wiring diagram I see there is a ETR switch between the a/c control and the relay. Does anyone know anything about this item and where it is located? Or any other advice on this issue?

Any guidance is extremely appreciated.