or ... you could just measure the resistance of the sc clutch (that is, I could have .... : )




I measure (with a very accurate meter) 3.89 ohms (on my slk32) .

At 14volts that is a hair over 50watts. The duty cycle being low, you may be ok with a 4 ohm 50 watt mounted away from anything combustible : )
http://search.digikey.com/us/en/prod...4R0-ND/2020187

EDIT
the manufacturer (of the above power resistor) states the following:
Power rating: Based on 25°C free
air rating.
Overload: 10 times rated wattage
for 5 seconds.

this part seems like it would work fine


EDIT 2

here are some better choices ... priced reasonably and aluminum cased with mounting holes
http://kr.mouser.com/Passive-Compone...sistor&FS=True
Chris