well, i don`t know, drop the starter, wire it to a good battery and make sure it turns as it should, he says the ignition switch is new but is it really working? mine has to be turned and pushed really hard sometimes to make good contact, he has an auto tranny, is the neutral switch really working?
the problems seems very straight forward to me...
But, it's intermittent. That's why he needs to narrow it down by watching the voltmeter.........
If he pulls the starter and it spins, what does that tell him? It's spinning now, but wait, it does that most of the time.
The test above will also help pinpoint a bad NSS.