I'm afraid I'm not that familiar with the Vette circuit.

The diode is there to bleed off voltage to ground when the system is turned off.

I believe the pressure switches are just in series with the AC request circuit - the two-pole switch in series with the power to the AC compressor clutch, the single-pole switch is the ground. The switches protect the system from pressure too low (liquid can reach the compressor inlet, hydrolocking it) or too high (blow out seals). It is possible to run the AC without the switches if you "hard wire" it. One terminal of the clutch electrical connector gets the 12V, the other goes to ground.

 

The mysterious (to me) rounded plug which reads 4-6 ohms that previously plugged into the back of the fbody ac unit, is I believe and verified (five7kid) is the high pressure switch. The c-4 corvette's harness and switch plugs into the high* pressure tubing on the lower pass. side of the C-4. The c-4 also has a larger plug (olive green and black wires) that looks identical to the low pressure plug on the evap, but this plug is next to the smaller high pressure switch on the tubing.
Since my harness is Fbody, I don't have the lower larger plug. However, I am wondering if I could scalp some tubing from the boneyard that would have the High pressure adapter (for the smaller plug). If so would it work? and if so, what GM model should I be looking for? The most convenient may be a swapped out cannister that has the high pressure provision, therefore avoiding monty python style tubing. I am on the right track? Incidently, I recently had success isolating, identifying and fixing the ground that was overlooked by the guy that did my swap. That freaking ground wire was hidden behind the harness in the most difficult place to reach. So I have blower working, but the AC-Heat controls are defaulted only to the defrost. I am hoping fabrication for the high pressure switch will solve this.

Thanks in advance.