If you are unsure which wire is which coming out of the electric fan, find the fan manufacturer's supplied wiring diagram. ... The Right Way to Hook Up a Relay to 12 Volt Power.

Industry-standard ISO mini relays are common and affordable. A 12-volt, NO/NC, SPDT version like this one (Hella PN 007794301, $6.38 at Summit) can control both normally open and normally closed ...