Originally Posted by Miata 5.0

As an aersopace electrical engineer that has seen it all, your problem is quite obvious. GROUNDS! There is only one thing that universally and intermittently cuases symptos like this. THe need to go through every ground point on the car (there aren't that many) and measure the resistance between the wire and the frame, then wiggle the wires and look for fluctuations. Take it from me. Lord knows we can't have aircraft "shutting off" due to electrical problems. I hope this helps.