6 lights at 55 watts (min) and 12.3 volts is 6 * (55/12.3) = 27 amps

15 amps for fan, 20 amps every thing else,    = 62 amps.....

62 amps at idle speed sounds about right............


With 4 gauge, you'll  won't lose 1.1 volts, probably about .4 volts