1993 Honda Accord Shuts off while driving

Every couple of months the car shuts off while driving, as if the key was turned off and starts up an hour later as if nothing happened. All the electrical systems are still working, (radio, lights, dash lights, etc.) Replaced main relay and ignition coil. Dealer states system tests and inspections, all working normally. I've read that the problem could very likely be with the ignition switch. Is this more likely than the fuel pump? If so, how would I replace the ignition switch? I don't have a diagram for this.
Thanks,
mljohnso