Electric Fan thermostat mounting location question

[evolve520]

I have a 350 in my truck and want to put an electric radiator fan in. I have all the parts but I'm trying to figure where to mount the thermostat sender. I see a "port" on the driver side between plugs 1 and 2 and another on the passenger side between 3 and 4. The pass side has a thermostat in it with a a wire I assume is tied to my temp gauge. The one on the driver side has some kind of brass sender in with no wires hooked to it. Is that a good spot to put the new thermostat for the fan? Thanks,
Jon