Voltage, Regulator, Coil, Ballast, MP Electornic Ignition, Standards.

I don't know about Barracudas which had the tachometer, but my 65 Dart has the "5V" reg inside the fuel gage. It is an archaic thermal-mechanical switch that modulates on and off, averaging to ~5 V. As most do, I disabled it and installed a $25 electronic Vreg. Search "Plymouth" and "voltage limiter" on ebay, plus posts here. In later cars (my former 69), the Vreg was a separate shiny rectangular box that plugs into the back of the cluster circuit board.