At the back of the switch , pull the brown/blue wire ( feed from battery
), pull the white wire ( goes to ignition system), join these together.
If you have an ohm meter, check the resistance between the spades at the back of the switch, it should be zero when " on " , infinity when open, if you see wavering numbers when on, its defo the switch.
Also , open up the fuse holder in the brown/ blue line , give it some love, clean any oxides off the contacts .
Get a #78 drill, they are not expensive, buy more than one. If you have an AMAL Concentric
this is an essential tool.
1971 BSA A65 workshop manuals are also still available. try e bay.