Like said , check the connections and grounds. Back in the 70's, I used to work on plenty of KZ650/750's that had ground connection problems, we at the dealer knew this, but customers go crazy trying to diagnose theose electrical problems. At any connection ,you can do a voltage drop test by setting your voltmeter on DcVolts, and placing one probe on one side of the connection being tested, and one probe on the other side of the connection, then hit the starter, if you see anything above about .2volts, you have a weak connection. A perfect connection would read zero volts across the connection under a load. This works on testing long sections of wires too, but you have to have power going threw the wire, to test it. One way to picture this in your head is,when you put a meter on each terminal of your battery, you get 12volts. That's a 12volt DROP between + and - of your battery terminals, because there's nothing but air between the two battery terminals,100% bad connection=12volt drop. Also do the load test on the batt. ,there's a good chance it's on it's way out.
1984 Goldwing Aspencade