Slick 60's

About the last time I drove my fully restored 66 last year I turned on the heat and fan for a bit. When I did this I noticed a pretty powerful spark coming from the hole the switch shaft goes into (this is the combo switch...turn the knob for fan speed, pull for defrost (I think).) Anybody have a clue as to why a spark would come out here? My own suspicion is that I may not have the switch properly grounded...but then again, how would it be grounded? (I'm thinking out loud here.) The vehicle was fully painted and I believe I put this switch into a nicely painted hole...so perhaps it's simply needing to be grounded? Beats me. Any clues are most welcome.
Thanks,
Ron

50 year old switch.....
Contacts probably not the best
..........
Just like touching 2 wires together to 'test' a fan motor
A contact can create a spark....
.....
I'm guessing you noticed this when it was kinda dark ?
As long as the switch doesn't warm up during use
I would say it is safe

That all makes sense. It doesn't get hot so that's not a worry. Perhaps I'll see if there is anything I can clean on it, clean up the contacts. Thanks for the input.