This is a close-up view of a GM HEI four-pin module. This particular HEI module is for a 1975 Corvette, purchased from RockAuto. Of course, you can also find these everywhere in the junkyard. Each of the four pins is marked with a letter. The W connects to the orange or yellow wire on a Ford or Chrysler distributor, while the G pin connects to the other wire to complete the circuit from the pickup. The other two connect the C pin connected to the negative side of the coil and the B terminal to the positive (+) side of the coil.