[Davidf]

Well, I cannot argue about your logic on the low level switch. But it can be of use if you have a catastrophic oil leak and get a bit of a a warning before you loose pressure. I will probably just keep the circuit and connector in the harness for possible future use.

As for the a/c, my truck has factory air. And I will keep all the interior components. But, I want to use the donor compressor, switch from R12 to R134a. I also want to switch from POA/TXV to accumulator/Fixed orifice tube (which will require a new evaporator). So, makes sense to keep high and low switches from donor is what you are saying. The way I understand it to work is that I will wire my existing compressor wire to the a/c request line on ECM (I think this signal goes through the high pressure switch). ECM compressor control will energize relay to activate compressor. And ECM low pressure cycling switch input will go through low side switch to ground. Easy peezy.

This is fun, learning a lot so far