Sport Rider, I'm not an electrical guy either.
I just realized that the plug {you may be referring to?} is the plug at the fan?
If yes, that is probably not the problem. Problem is probably at the thermostat/switch.
#1} Check voltage on both sides of the fuse to eliminate that as a problem.
#2 Assuming you have voltage at both ends of the fuse, the problem is probably the thermostatic switch.
That thermostat/switch is located on left/rear side of the radiator.
I think it has 2 wires plugged into it.?
If yes, disconnect them from the thermostat and short them together.
Fan should run.
#3 If no run, check voltage at those wires and report back...
NOTE: The fan is battery powered, {not switched power} and shorting them together will make them run regardless of the switch being turned on.
Ride safe, Ted
what I did was make a small jumper wire with bullet plugs which match the wires into the thermostat/fan sensor. testing voltage at both ends of that jumper after installing, I got a reading of 11.9. I tested the plug where the fan wire connects to the wiring harness which is up under the neck of the bike. testing the voltage there was a reading of 11.9. but when I plugged the fan into it, nothing. same results for the fan on the bike and my extra fan.
since there was no battery in the parts bike, I swapped the battery over from the project bike. I plugged in my jumper wire across the thermostat/fan sensor. plugged in the spare fan to the harness connection and it works.
in testing both of the fans, I also made a test wire set. basically mini jumper cables. I used nails on the end of the wires for probes. the other end of the jumper connected to the battery. when I used this to test the fan on the bike and the spare fan, both work.
as Rich said, it's a simple circuit. my only guess is that something in the harness is bad? maybe something is pulling power away? maybe the ground is screwed up? the ground wire is the only oddity of the circuit. red/white wire into the sensor. blue/white wire out of the sensor. same blue/white wire at the fan plug which gets joined by a black/yellow wire which is a common ground.
I tested the power at that plug connecting to the two wires in the plug and got a good reading. I also took a reading with the blue/white power and grounded to the frame. good reading. plug the fan in...nada.