damn i suck at communicating. and i leave shit out i take for granted people just do....so please be patient
building a proper inline hose tee to put in close to the block is understood right?
say a 1/2 x3/8 x 1/2. two half inch npt pipe hose nipples and the 3/8 npt sensor goes in the 3/8 npt part of the tee.............
........... or just get a 1/2 or 5/8 tee and put the proper 3/8 bushing in it......
important thing here is you have to ground the tee, usually use a camp and a wire to the block
so, with that switch in the properly grounded tee, or in a 3/8 port in the block, you run a wire on its single terminal right to the ground side of the relay that runs the fan for a simple automatic fan switch. this assumes you know how to wire a relay
assuming a single speed fan, use a regular 40 amp relay....for a low draw light and small fan.
if it is a oem or large fan i suggest two relays to split the load.
if, like you appear to want.....you would like to opt for a switch to allow the previously mentioned full control over the fan, get a 35 amp 3 way switch.
run the wire from the fan temp switch to one leg of the 3 way switch.
ground the other leg of the 3 way switch
and run the ground from the switch side of the relay/s to the middle post of the 3 way switch.
so thats two wires to run from the engine compartment, both grounds.
in the middle "off" position the fan is dead.
at one "on" position it will be fully auto whenever the power of the swicth side of the fan relay is activated.
at the other "on" position it will run till you turn it off or the power on the switch side of the relay is deactivated.
i am doing my best to describe this, but i fear i fawked it up again.