Two-speed (1977 on)

Hover over a wire to confirm the colour

I don't know the actual resistance and wattage values of the dropper resistor, but did some tests to see what sort of values they might be. I put a standard 3 ohm coil in series with the motor and it seemed to drop the speed by about half which would be about right. I then measured the voltage across it with the motor running at this sped and got about 5v, which at a system voltage of 12v (engine not running) is about half voltage which tends to confirm what I heard. Wattage is calculated by multiplying the voltage by itself and dividing by the resistance i.e. 5x5/3 which gives 8.33 watts. You would need to go at least 10w for a safety factor.

If you have a 2-speed you can measure the resistance by putting an ohmeter between the green/yellow and green/brown wires with the fan switched off, and putting a voltmeter between those two wires with the fan switched to slow.

You can only calculate watts by measuring the actual resistance of and voltage across the resistor in this way as the motor has a non-linear current/apparent resistance characteristic that varies with its rotational speed. You can't measure motor resistance and use that in any calculations.