A/C Compressor not coming on - 1970 Jimmy

[Resto-Rat]

I am having a problem getting the A/C compressor to engage. All original A/c Equipment appears clean and in good condition. I am assuming 12 freon

I have rebuilt the dash control unit and all of the ducts. All OEM and working fine. The switch turns on the blower at all levels just fine. Blower blows strong.

But the compressor is not coming on to make cold air.

The pulley spins. I have pulled the green and black connector off and when I ground the black spage, and put power to the green side, the clutch clicks just fine. So I think that is engaging.

Is there a way to test the green and black wiring to see if that is good?

There is a strange looking little jumper in the plug of the black and green connector that looks like a little resistor? (Picture posted) Cold this be fouling something up? Does not look original.

I see posts to jump the terminals on the pressure switch to see if that engages the compressor possibly indicating low Freon, but I don't know where to look for that. I have posted a picture of one switch looking think but not sure if that is it or not.

I have researched all the threads I can find as well as the internet on testing low and high pressure switch. I am not an A/C guy so I don't know where to find the switches. I see nothing anywhere under the hood, and I had the A/C blower completely out of the dash and only saw one connector on the back of the blower box that I assume has something to do with the heater?

Can anyone tell me where the low pressure switch is? There is a 5/8 ish plug on the back of the compressor but I pulled that off and it has no wires to test like I see on other internet posts.

Ideas?

Sammy