One issue is that many machines have very poor wiring, especially the connections. With modern day crimp connectors it is easy to do quick repairs, some of which are very weak (and look absolutely unsightly on the old bikes) This unfortunately is where most have problems ..........Also the importance of good earth points is critical, this was something very lacking on most all early machinery, the manufacturers struggled to come to grips with the importance of this as well. Because so many owners have equipped their bikes with all manner of electrical devices, the load on the electrical system is under much more strain. The need for proper connections is a must, and soldered joints give excellent results. Multi pin plugs are ok so long as the quality is good, it is not uncommon for the wires to separate from the pins when the plugs are separated, especially on small plugs where the male/female pins are very small.........You actually need a special crimping tool to do some of these plugs..........The wiring is probably one of the most neglected parts of old bikes.