Here are the specs you wanted:

Original sensor for your chassis was Red w/R12.

Sensor S/32- Aux Fan -High Side Pressure

Red :
Cut-in- 16 Bar +/- .5 Bar
Cut-out- 12 bar +/- .5 Bar
Green:
Cut-in- 20 Bar +/- .5 Bar
Cut-out- 15 Bar +/- .5 Bar

So , Red S/32 will give you the earliest and longest low fan with R12.
..and you can still do a cabin toggle across those two pigtail terminals if you want a manual over-ride w/o affecting the stock circuitry.
Tapping into the circuit there will eliminate the problems of any additional relays or fuses b/c you are simply using the original circuitry [ relay , resistor, and fuse ] that are already there.
Slick..........

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A Dalton