Hi I am trying to figure out how setup a variable power switch for a series radiator fans. I do not want to use a thermostatic control box, because I am cheap and i like the simplicity of the switch.

I would assume just use a dpdt rocker but I can not figure what magic box it should be connected to, do i need to use multiple relays with a jumper wire, a solid state relay?

Switch should turn fan off, turn fan on at reduced power (50%), turn fan on at full power. Switch should only power fan when the ignition is in the on position. Fan runs on 12vdc at 15amps and should use a 30amp fuse.

 

Not sure how you can decrease the speed of a fan, I would think you need some sort of resistance to lower the voltage.
I have seen electric fans with two speeds, that will have three wires, ground, 1st speed and 2nd, if that is the case, two switches will be needed to activate one or another, or a switch with two on positions will do as well

off course Relays will be needed to handle the load