350 eats ignition modules. 1979 Truck

I have an old 79 3/4 ton truck that I feed hay with. For years now it has burned out ignition modules. It used to be one a year, now it is going through them at a hell of a clip. It has a 350 small block with the early HEI ignition in it. A couple of years ago I replaced the entire distributer in an effort to cure this problem. It hasn't helped. The truck has a large electric over hydraulic bale spike on it. I have a large sealed gel cell battery in it and a high output amp. Any ideas as to what is causing the problem?

Welcome to AF. Make sure you are not operating over 15v out put, also the engine is well grounded and the module is is mounted in the dist with the special heat sink grease.

Thank you for the reply. I am beginning to think that it is a grounding problem. I am going to test it out with an OHM meter per a friends advice.