Check the wiring to the fan...
1) disconnect the connector to the cooling fan relay, should be 4 wires, yellow, black, green/red, yellow/green.
2) Put a test wire between the yellow/green and black pins of the connector, turn ignition on.
2a) Fan on verifies the fan power wiring, you probably have a bad relay
2b) Fan off means wiring or voltage issues
2b1) Ignition off. Remove the test wire. Use ohm-meter to verify relay connector black wire has continuity to ground - open means damaged wire or connector or ground connection
2b2) Use ohm-meter to verify relay connector yellow/green wire has continuity to cooling fan connector yellow/green wire - open means damaged wire or connector
2b3) Use voltmeter to verify cooling fan connector yellow wire has 12 volts when ignition is on - 0 volts means damaged wire, bad fuse,
If all this testing passes, and if you disconnect the wire to the temperature switch, and the fan does not come on, then the relay must be bad. Sometimes relays will click and still be bad internally
Yeah, I used to write electronic test procedures for a living for military avionics systems, I could easily make this a 3 page manual
Chris