BB this is a common issue,, There are at least 4 causes of that...
1: There is a virus among us that likes to live in current rich places like the electrical connectors you describe, This first came to light in the early days of Home Computing when most of the boards were heavily socketed. Simply re-seating cards and chips fixed many a computer.
2: Vibration
3: Mositure getting to the connector and causing tarnish. (Corrosion).
4: Actually it's OXYGEN from the air that does the damage in 3. No moisture needed, water just accelerates the process.
I will tell you how to fix a switch (And I will tell you if this works,, You might want to buy a lotto ticket,, I've had it work twice so far). (Still have not won lotto though).
Remove power from the switch, (Drop the load off, pull the fuse, or simply disconnect the switch from everything)
Cycle it like 50 times (more, less, exact number not important)
Return power/load/to circuit and see if it works.
Most switches are "Self Cleaning" which means the contacts rub against one another to rub off tarnish, but sometimes.. The tarnish is too much, When this happens they arc and "Dirty" themselves as fast as they clean.. So removing power, stops the arc, then the normal wiping action cleans the switch.
Like I said, had it work 2x times so far, ONe was my USE/STORE (Battery disconnect) switch, It "Stored" (disconnected) Just fine.. but alas "USE" did not work.
