It's baaaack! HELP

Mine was doing a similar thing with the tach once. It would be idling and all of a sudden the tach would blip to 0, cough, jump back to 700 and idle fine. Mine turned out to be the wire for the electric choke assist that gets its power from the ign circuit, I had knocked it off when messing around under the hood and the 12v source was touching the ex manifold every once and a while.

If the only thing that you haven't changed is the switch and all you have to do to get it running again is wiggle the switch, then it's most likely the switch

But, it sounds like you already know what it is but don't want to change it ( ignition switch ).
We all have done it at one point..at least I have.. ( changing the "easy" parts first because the part we hope it's not, is gonna SUCK to fix ) .... it's like changing a water pump and/or thermostat when we know ( and everyone else says ) the radiator is plugged...

Nuker has some good troubleshooting advise, and I've said it in the past, electrical gremlins run in fear from a methodical approach and repeatable processes. Unfortunately those are very time consuming...