Head to Firewall Ground Strap.

[jinksater at yahoo.com (John Inksater)]

I experienced the intermittent problem of the ignition shutting off anywhere from a fraction of a second to several minutes but never, of course, near a garage.  After looking at Hall senders, distributers, coils, ignition controllers, wires (you name it) replacing the ground strap cleared up the problem.
 
 John