Well then, here is an easy test for you.Yup. Both of em plugged in.
Unplug the connector from the thermal switch on the lower radiator.
Use a paper clip (or something) to bridge the contacts in the loom-side connector.
The fans should start.
If so, it indicates that the thermal switch is not closing when the 'switch temp' is reached.
If the fans do not start, there is a problem in the wiring somewhere.
While the switch is disconnected there should be ~12 volts on the Black/Red wire.