Westinghouse WD 12 Thermostat

[Marines27]

I need to replace the type M thermostat on my 1952-ish WD12. I have a new stand alone thermostat, but need to know which terminal studs the two wires from the thermostat should attach to. The  Westinghouse manual shows the original goes to the #1 (red) and #3 (black) terminal studs.  Also, do I need to remove the non-functioning, original thermostat (stuck closed; compressor would not shut off)? Thanks

[WDG]

I'm sort of guessing, but if you have four terminals, the best way to check it out is to get a continuity meter and see which terminals open and close when you turn the knob.  You don't HAVE to remove the old one, but why leave it there?  I would remove it, myself.