Painless it. Having the back of the dash looking like spaghetti is no fun if you need to trace something. All those crimps are just begging for some salt spray to corode them and make more intermitent problems that you ever want.
Replacing the ignnition switch shile you are at it isnt a bad idea either. hit an autozone and get a new one, cant be that expensive.
I had the problem of engine staying on in my buick, and it was cured by going to a 1 wire alternator. The stock regulator and wiring didnt like what I was doing to the ignition system and other parts of the wiring. With a harness hacked up, I would imagine something might be messed up with the wiring to the regulator.
I assume you just have the distributor, and a coil, no other mods to the ignition system?