your resistor has to be able to handle the wattage.

amps = 100W / 12V = 8.3333A

so the 10 watt resistor is meant to check for under an amp.


http://www.amazon.com/Chassis-Mounted-Aluminum-Wirewound-Resistor/dp/B008IE2IWI

7 bucks for a 100 watt to take up to 8 amps.

http://www.ebay.com/itm/like/231092951644?lpid=82&chn=ps&ul_noapp=true

1k watt for 35 bucks.
80 amps.