Radiator fan won't come on my wifes 2004 ford mustang?

Radiator fan won't come on my wifes 2004 ford mustang? - 1

My wifes mustang (2004 3.8 v6) radiator fan is not coming on when it gets hot or when she turns on her heat/ac. The fan is less than a year old and was expensive and looks in good shape. I don't think it is the fan thats the problem, but maybe a fuse or faulty harness (power cable running to fan directly). I don't know if this is something that can be tested for functionality or replaced. I have a feeling that the last shop just saw the fan didn't come on and assumed it was a bad fan, replaced it and hooked up the harness at just the right angle for a good connection or something like that since this has been a recurring issue. We have flushed her radiator, refilled with fresh coolant, replaced hoses and thermostat.

The fan itself likely didn't need replacement, but it's a good bet for the garage because people rarely ask them to take it back out.

There's a few things they should have done first:

1. Fuse. Check it.
2. Unplug the harness at the fan and make sure you get 12 V between the two leads. If not, verify that the relay is working.
3. The temperature sensor. There's two wires that connect to the thermostat cover - unplug them and bridge the two wires together. The fan should start spinning. If it doesn't, the sensor of the sensor wiring may be faulty.

Hi so does it actually get hot enough as most female drives never get tehcar up to a working temperature as the always drive so slow. Hence the mayonnaise in the radiators.

Might be the thermostat