Leaderboard

Are you talking about an electric heater? if yes its likely too much current. There might be 10 amps of available current coming out of the rectifier that isn't already claimed by the ECU and factory lights. 10 amps @ 12V = 120 Watts, which is about what an electric heating pad runs. If you're talking about a fan for a engine coolant based heater it's probably ok. If you have accessories and the running voltage is below 13.5V you have too much stuff attached. If the battery light comes on it means the battery is actively being discharged while running. Stator based charging systems on these things and tractors etc are really meant to power the ECU and factory systems not to provide a lot of extra power for other stuff, it's not like the alternator on a car.