if the plug came with the alt, it may have been intended to have the wire added or not depending on the particular applications wiring, every DA plug I've seen has had 2 wires on it ... the excitor needs to be on a switched terminal, like the coil ... no idea of the diode number but I'd expect a parts store to know what you need there, or you could just put an indicator light in line, which serves the same purpose .... someone else here may know more specifics about the diode and wiring
Bill
