You could have any one of a dozen problems. I put no trust in aged wiring.
When I restored my two bikes I bought a complete wiring harness for each, made sure all grounds were on bare metal, tight, and insulated with dielectric grease. Every connection was also made tight and fitted together with dielectric grease to avoid any corrosion. I have never had an electical problem.
I suggest you do the same. It will save you a lot of headaches in the long run.
Probably not what you wanted to hear, but for about $100.00 you will never have to worry about your wiring again.