Re: car shuts off at random?
Coil is located in the top of the distributor cap, under the wire holder cover. they can have problems as they fail, and testing is to remove the coil from the cap, and take it to an auto parts store that has an off vehicle electrical run tester. Let it run, as most epoxy filled coils have problems when they get up to, or near operating temperatures.
If the coil is proven to be bad, or, going bad, it can fail the HEI module that is located under the cap and rotor. A coil that is going bad can fail a few modules before it fails, and won't give you any indication it is the coil causing the problems.
Also, make sure all the wire connections are in good shape, and clean/tight as well. Ground from the battery should be from negative on battery, to engine, and then, smaller wires between engine and body. Lots to check, not hard, though. Main things to check are the coil and module, and to ensure all connections are clean and tight. HEI runs on a full 12 volts, not through a points ignition porcelain ballast resistor, or resistor feed wire.
First quick test is when it fails, use a jumper wire with alligator clips between positive terminal on the battery, to the BATT terminal on the cap, this bypasses the ignition switch and wiring, and see if the engine wakes back up.