Black powermaster switch nos eBay

It's the low pressure switch that screws on the accumulator that kicks the compressor on.
 
That's an A/C switch according to the auction.

I think the powermaster pressure switch has male threads sticking out (seems like it's an O-ring seal). It's been a while since I removed one.
 
It has two prongs like a plug but the rubber cover boot that covers the orings seems to be already on the switch. FTI in between the prongs on the switch is a slotted screw that allows for adjustment of the kick in or kick in pressure of the low side for the compressor.
 
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