I know this may not have any relevance but the bike is 50 years old and I has sat for the last 25. The bottom oil pan has never been removed. So I have no idea how much crud is sitting down there. Would there be a potential issue with lack of oil pressure buildup due to the condition of the pump?
This has a LOT of relevance...the contacts inside these oil PSI switches are anodized copper, and that anodize had a 10-year-life rating. After that it started letting go of the copper surface, and the loose anodize, which you often see on the outside of the engine cases as a white powder, makes a nice insulator! It also melts at high temperatures, which the original manufacturer (most were from TEC) counted on to keep the switch serviceable with the low current of a lamp.
So, you sort of have 2 options:
1. If you're sure you have good oil pressure, run it for a few months to see if the anodize will melt away from the contacts inside the switch and restore the operation again. My 750 has gone thru this cycle several times: I finally changed the switch for a new one in 2013, though.
2. Disconnect the switch (use the little bullet connector near the drive sprocket if this is a 750, it's easier to get to than the switch) and hook up a 9 volt battery, (+) to the switch and (-) to the engine (use a clean bolt for this ground, like a starter cover's bolt head) for about 5-8 seconds to heat up the switch's contacts and try to melt the anodize powder away. This will kill the battery, which is intentional: this action won't start a fire...Then plug the switch back into the bike and see if it works. This won't burn the switch contacts: they can withstand 5 amps and the battery can only deliver 0.3 amps max.
3. Replace the switch. The ones from PartsNmore are good one, and they also sell a nice harness with cover and wire to go with it!
