What's the procedure for replacing the oil pressure switch? Do I need to drain the oil first, or is there no oil at that level when the engine is not running? (this is on a '73 914 1.7L by the way)

No oil up that high when not running.

I would think you would be able to change it with out draining the oil. If uncertain, just unscrew it slowly and see what happens I guess, but with it being on top, I doubt if it is an issue or just do it when you get ready for an oil change?

Maybe this article can help?

http://www.914club.com/bbs2/index.php?showtopic=91264

Yeah, actually I didn't even realize it was on the top of the engine... pretty sure there won't be any oil there when not running. I'll replace it tomorrow and report back.