Bill,
I usually find that most MSD problems aren't.

Usually it is;
noise entering in the low voltage trigger wires because they run in side by side with higher voltage wires.

Crank Trigger Pick-up Gap is too wide, causing hard starting and kick-back.

Distributor rotor is not correctly indexed and in phase so the wrong plug is getting the spark to the plugs instead of the #1 plug. It only takes appx 30 degrees off to do it.

Distributor rotor was put in phase for a nitrous engine when runijng it on motor and gets big time out of phase when the retards are hit. Phase the distributor and rotor together in the degrees of advance the engine will be mostly running at. Do not set rotor distributor phase at TDC like some people do.

Not checking and re-setting the timing when changing from one box to another box. Even with same model number each box will be different.

IF you have a Digital Box from MSD or from anyone, You need a Voltage Spike Protector called a Noise Filter in-line between your battery and your box. Voltage spikes of instant high voltage or amperage can kill a Digital Box. They can kill your computer at home too, that is why you have it hooked through a Voltage Spike Protector that was not supplied, You bought it extra.

The Older AL and Regular MSD Boxes were very suseptable to water damage, from pressure washing the engine or other sources.

ED

And still today you see so many ignition boxes mounted under hoods, on fenders and just in place they should not be.....

Glad some good advice fixed the problem.