[J57ltr]

Use a minimum of 8 gauge. RC cars have very short wire. The longer the distance the larger gauge wire you have to use to handle the power. 8ga is good for about 10 feet and 50 amps continuous. Current draw is basically the RMS output of the amp (all channels) in watts then add about 60% more to that to account for the inefficiency of the amp (unless it’s a class D, then use 40%). So you have a 400 watt amp plus 240W for losses which is 640W of power required. I divide by 12V to end up with 53.3 amps at max power. Amps don’t put out their max power very often and you will probably see about a 15 amp average draw. Also make sure your ground is solid (and same gauge) on clean metal or you will have alternator whine. You didn’t say what the amp was but if it is a quality amp then this is about what you will see. I can tell by the wattage rating that’s not a real high quality amp, and is not 1 ohm stable, but use what you have I guess.

Jeff