The 3 wire radiator temp switch and the 2 wire freon pressure switch can be look at as sperate independent triggers

with the 3 wire temp switch disconnected the jumper wire on the 2 wire freon pressure switch you will independently get low fan mode with key in run position

The 4 wire freon pressure switch which you can test jumper you will get high fan mode between wire White / Blue and Black ( there are 2 black wires to ground and either one makes no difference )

 

The jumper plug for the TSB will be on the freon pressure switch which will not click to the point where you can feel it with the AC operating to give you freon pressure above 12 Bar

 

Is there any circuit at the fan relay that gets activated by the key going to run?? Only thing I could figure out so far is circuit from TSB goes to 0v in run pos.

 

Looking at point 9 double hash stop sign when the key is in the run position ...............................

Point 9 is a ground command path

So the fan control relay module is putting out a feeler voltage on wire Yellow / White

Your observation of it going to 0 V ( since it is grounded out on the Yellow / White wire ) is correct only with the key in run

They don't use distantly different wire colors so can be confusing on which side of the 2 wire pressure switch it is referencing / location

 

So in all likely hood my brand new relay is already bad

 

If the Papa Indy 59 connector pin 8 has corrosion it would not be able to get to near 0 volts on your test and give in the end give you low fan mode

Corrosion would keep the wire not feeling a ground and would keep you from having low fan mode

 

not quite yet but you know bad parts out of stock