Watts = Volts X Amps. If a 1 ohm resistor is flowing 5 amps of current it's dropping 5 volts across the resistor, and producing 25 Watts of power (heat). The same resistor would drop 20 volts and create 400 Watts with a 20 amp flow. The trick is to figure the maximum current an accessory will draw and size the resistor wattage accordingly. Using a too-small wattage rating will result in resistor overheating and burnout. Higher wattage capacity on a voltage-dropping resistor is always better, as they produce a LOT of heat as they consume voltage.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!