First thing I would check is the large Block connector under the tank near the Head-stock. With age all block connectors are prone to corrosion on the spades and sockets. Using a small flat-blade screw driver with some 500 grit wrapped around it I carefully remove all corrosion by scraping and spraying Contact/Switch cleaner on them. When satisfied they are clean metal I blast with some Carb/Brake cleaner(Wilkos Supermarkets good price for a big can) and let evaporate.
I then treat them with ACF50,
https://www.ebay.co.uk/itm/ACF-50-AN...MAAOSw4SlV71bz
Also check the Wiring loom around the front of the bike for chaffing.