Hate to start another thread ... but.. help !

I would monitor the voltage from coil+ to BATT- while driving. When it dies, see if that voltage difference goes to 0 V. If so, suspect the ign switch, bulkhead connector, and ballast. Also, check that your MSD box has a good ground. A dedicated wire beats a rusty screw every day. A $5 in-line spark tester is invaluable too.