A few items that need to be checked:
First, do the simple thing, check to see if any fuses are blown under your shelter. If no blown fuses go to the power side.
Is the fan working? - With the bike and power off, see if you can spin it by hand (checking for a burned out motor bearing, it should spin freely). If yes check the power to the fan.
Pull the plug off of the sender (follow the wires to the end from the fan). Turn on the power and put the negative on the chasis and the positive in either pin. One of the two wires will have 12 volt power.
Next, check to see if the fan will work with power. With the plug off, I use a two conductor wire and put one conductor in each hole. Then take the wire either to your battery or a spare battery and see if the fan will work with 12 volt power.
Next thing to check is the brass on/off switch. This is a real simple switch that has a normally open circuit. The power goes in one wire and is normally not able to make contact to finish the circuit until the switch reaches about 195 degress and will complete the circuit turning on the fan. That switch will need to be tested.
To test the switch, drain the coolant halfway down, remove the switch (I use a large socket, cannot remember which size, but you can figure that out). Make up two wires and connect them to the switch and the other end to a continuity tester. Put the connected switch into a pot with water and turn on the heat. (I put a meat thermometer in with the water to watch the temp rise) When the temp gets up to around 195-200 degrees (May go as high as 206 degrees), the switch should close and the continuity tester will show a connected circuit. If the water boils for more than 1 minute and the circuit doesn't close, the switch needs to be replaced.
Gerry