Since about 2007 or so, EMGO has been marketing the lighter-duty CB350/450/500/550 switch as a CB750 switch by just changing the connector. They outwardly look the same: inwardly, the 750 contacts (and the BLACK wire) are sized for 15 amps, where the other bikes are sized for 11 amps max. I have seen MANY of these switches fail. A local Honda shop was buying them and putting a Honda logo on the bag, writing the 750 part number on it, too, and selling them: I've seen 4 of these in my garage since then with melted wires, contacts, and/or the BLACK wire unsoldered from the back of the keyswitch from the overheating.
This is just another example of Chinese reverse-engineering by unknowing (or uncaring) designers who see an outward similarity (of the keyswitch) and make a bad product out of it.
To make matters worse, Honda quit supplying the proper keyswitch during 2008: I don't know if they have started it back up again or not.
To resolve the problem completely and on the safer side, I started making "relay kits" for the main power feed on the bikes that I build. I know that some day in the future, an owner will wear out his keyswitch (the tumblers do wear out inside) and get a new one, only to find this new problem. The relay gets installed either under the seat (K models) or in the headlight bucket (F models) and the BLACK wire at the keyswitch gets clipped, just on the harness side of the connector. The BLACK from the connector now goes to the coil on the relay (other side of coil to GREEN wires). The clipped-off harness BLACK then goes to the switched side of the relay. The input (or 'supply') side of the relay goes back to the main fuse, and I usually run this as a 16 AWG RED wire along the harness on F bikes, or just splice in at the fuse for K bikes (under the seat, at the fuse).
This way, you can use the crummiest, cheapest, made-in-Lower-Slumbovia keyswitch, and the bike will work fine. It's becoming more common, so I added this in the Electrical section in the book.
