If you follow avguy’s Post you can verify if the fan has the issue (excessive friction on bearings/bushing or damaged coil) which would cause higher current draw. If that works okay then you can rule out the fan and take a look at the wiring. To check the resistor you can disconnect the fan connector and pull fuses for fan hi&low. Measure with your multimeter on ohms and see if it is open (at these currents the resistance is going to be very low). Alternately , you could measure the voltage drop across the resistor with the fan low circuitry running and (I make an assumption here that fan runs around half speed) you should see around 6 volts across the resistor..

its possible your fan low low circuit could be defective and causing the fan hi circuit to cycle off and on more often than it was designed too(another assumption).

Cheers