You have to remember that the 500-watt rating is for sound power to the speakers, not electrical power used by the amp, unless that's what the manual says. The manual (or a plate on the side/bottom of the amp itself) should tell you how many watts of electricity it uses. For example, if it actually used 500 watts of electrical power, just divide that by the 12 volts of the car's electrical system to get the amperes, which would be just under 42 amps. Considering that ordinary house wiring carries a maximum of 15 amps, the wiring to the amplifier would have to be three times as heavy. That's not likely, is it? Anyway, the amplifier should have its own fuse in your car's electrical fuse box, so just look at its rating for the electrical amperes.