Fan Switch Relay

hi,

if the temp switch has two terminals, a spst switch across the terminals will provide a manual override.  if it has one terminal, a spst to that terminal and ground will do the same.

mark

This is how it is currently wired, will it work???

The one wire thermo switch goes to ground as the engine temp rises.  The way you have it wired, the fan will only work when the manual switch is used.  The manual override switch needs to be a ground source.  The diagram I have attached shows you one way to setup the wiring, the manual switch can be used before the thermo switch would come on, but once the therno switch goes to ground, turning the manual switch off will not stop the fan operation since the thermo switch will be completing the circuit. 

I recommend controlling the fan relay with a 12V ignition source, so that the fan will cut off when the ignition is turned off, otherwise, the fan will run until the temp cools and the therno switch deactivates the power.  Of course, if you want the fan to run after the ignition switch is off, then use a constant 12V source to relay terminal 86, but your battery will be providing all of the power once the engine is off, and electric fans pull a lot of amps, so your battery would need to be really healthy to repeat that scenario everytime. Personally, I wouldn't wire it to run after the ignition is off. 

Also, if you have air conditioning, the electric fan should be wired to run whenever the ac is turned on, regardless of the engine temp.  Its needed to move air across the ac condensor to cool the refrigerant and to keep the internal pressure down. This would require a second relay in addition to the one shown here.