Electrical Demon?

I'm in need of help. I have a fresh 360 build in my Scamp. I have a problem with the engine stalling out. At first it appeared to be heat related and I treated it for vapor lock. But then it started to do it cold and finally got to the point where it wouldn't even start. I discovered 2 spark plug wires that were melting next to the headers and possibly even arcing, so I replaced all the wires with new Accel 8mm wires and installed a new coil. It started and ran well for about 15 minutes and then stalled again. But at least at this point I could get to start again. I noticed that most of the times it stalled I wasn't getting spark from the coil. Tried a second new coil with the same result.

The one clue is that I had test light on the positive lead of the coil and without touching anything (ignition was in the run position) the light suddenly went from dim to bright. It immediately fired right up at that point. I'm getting 9.4volts at the positive lead on the coil.

The only thing in the entire ignition system that is not brand new is the ignition switch. Could that be the source? Thanks in advance