You have a machine that had the "Steve Charland mod" done to it in the past. In a nutshell, many Fast/Quick Draws give spurious 100 pt scores during player change that somehow comes from the 500 pt relay circuit as the drop targets are reset. This mod positively opens the 500 pt relay circuit when the P relay is active to prevent it. It's a good mod if your machine does this.

https://groups.google.com/forum/?hl=en#!topic/rec.games.pinball/xZ7rtFC0p2A

Your guess is as good as mine why there are no wires there now. Maybe a purist, albeit a half-assed one I would have to add, wanted to bring it back to original print, so he took out the wires, but then left the switch, just in case. Who knows - maybe someone had a coffee machine wired to it - people do strange things every day.

Yes it's kind of a mysterious thing and it's apparently a timing issue and it can be a bugger to get it working correctly. I know this because I had this problem with mine, and I fiddled with it for a while and just like Steve (who btw was no dummy when it came to pinball machines as I'm sure everyone knows), I could not get it to be fail-proof. So I added the isolation switch to mine and never had to think about it again.