The 81502 is Clock Wise Rotation. The 81602 is Counter Clock Wise Rotation. The increased output of the 20 Amp Pro-Mag was born of racers being racers; always asking for more power. This stemmed from drag racers that were using a 12 Amp system, but just didn’t require a 44 Amp system. The engineers at MSD found that with a few changes to the internals of the generator it would deliver the increased current through the same Electronic Points Box, PN 8106.
All three require the PN 8106 Electronic Points Box. The band clamp versions are equipped with a large Ford style cap while the Chevy version uses a 4-inch cap and both are topped with heavy duty retainers.