[Jack21]

The distributor wiring conventions have 2 leads coming from the distributor. These are for the magnetic pickup coil. + is purple, or black & purple, - is orange, or black & orange. The third wire is a ground that was used in some OEM applications. If you have a good chassis ground, you don't need it.

The distributor leads from the MSD should be identified by color in the schematic as to +, & -. The distributor leads out of the distributor should be similarly identified.

The MSD documentation should describe the symptoms of reversing the polarity. If all else fails, hook it up and if it runs OK, leave it alone. If not, reverse the leads.