I'm still working on this crappy mod. Bad enough it's compromised, it's not working as expected. I no longer think pin 10 is a ground, it's at 14 Megs to ground with a/c on. Pin 1 is ground, and I'm pretty sure Pin 10 should have power through the pressure switch in normal a/c operation. But instead, it's showing .75V. It could be that the system doesn't switch on until engine rpm is above 600, and the Klima is required for that. I have corrected my diagrams, and posted the latest but be aware that it's still work in progress:

http://www.peachparts.com/shopforum/diesel-discussion/386849-compressor-speed-sensor.html#post3735148

In the worst case, I can build a solid state circuit that can switch based on a .75V signal. It's getting to be a lot of work...