New harness? Best guess, you have mis-wired the Ignition switch. Something is on all the time. The tip about the battery cable is good one, Thanks Dennis. The tip from wirewizards is good too. Jim has, pointed you to some of the big current users as well. But the thing that can cause this if all else is good, the Voltage Regulator. Easy check? Take the wires off the genny. If the problem goes away, the cutout relay is probably stuck.
