Since someone brought it up in another thread...I have MANY Promag "bad plug wire" stories this season so far.
Behavior that you'd never suspect and it's the suppression core race wire that the electronic mags require. People don't understand that it wears out! It looks perfectly fine and good but electrically, it's a nightmare. It might check out fine and seem normal with the ohm meter, but when they're changed out for a new set, everything is happy and normal again. Even if you can't explain why, it's difficult to argue with results!
So, if your Promag ends up having strange timing and phasing issues that don't make sense, timing lights freaking out, points boxes not working right...save yourself some time and change the plug wires first!
Spud