The large post on the starter holds the cable from the battery as well as the large wire to the alternator, I believe that both of those are supposed to be red. As noted there are sometimes 2 small terminals usually marked "S" and "R", the "S" terminal is home for a purple wire that comes from the start terminal of the ignition switch. The "R" terminal was used on pre HEI ignition engines and was for resistor bypass, it allowed full 12v. to the coil for start up while cranking. Many stater solenoids now have deleted the "R" terminal.
Gus