After a fire.....

A fusible link, which a '64 probably had, helps protect against a direct short from battery to ground in the main circuit.

I know about those obvious fusible links in the later harnesses, and noticed my car didn't have one.
Got me curious where I saw it. Yup. Factory started using them in 1965 models. So your 64 would not have had it. :(
1965 Electrical Accessories & Service, Master Technician's Service Conference p.13