[patrickt]

Here's what you do: Hook a nice 12v test light to the small red wire that runs to the MSD box, along with a good ground, and have it hanging out of a very visible place like the corner of your glove box. It will light when you turn the ignition on and will go off when you turn the key off. Drive your car around until it dies again and immediately look at the light. If the light is off, then the problem is in your ignition switch or wire feed to the box. If the light is on, then immediately get out and check for spark (you're likely not going to have any). With a no spark condition and a confirmed 12v going to the MSD box you then proceed to the classic "no spark" diagnosis with a MSD box, coil, and distributor pick up.