[Wbulk]

The fan normally turns on when the fan relay is grounded causing current to flow through the relay to the fan. The ground is usully accomplished by the fan thermostat reaching the desired temp and then grounding, or a manual switch to turn on the fan going to ground.
Did you check to see if when they worked on the car they turned the fan thermostat knob. You can set those down to about 38 deg. I think. So, it would be on even when cold. Other than that check your two grounds one on the fan thermostat and the other that goes to ground from the manual switch.

Wayne