Hy Hydra1/2ton, if the black wire is a large gauge wire [which I'm pretty sure it is], it goes on the large terminal with the wire from the battery, the purple wire goes to the terminal closest to the engine block. The black wire is the one that brings battery power into the dash, where it can be distributed. The six volt trucks [which yours was] did not use a ballast resistor circuit, so if you go with the old points type distributor, you will have to install that circuit, for the best cold starting performance, hope that helps.
