Mercruiser Thunderbolt IV ignition

[caravelle 2000br]

I have a 1994 4.3lx Mercruiser I had the original ignition module fail I got a used one from my local parts house and installed it with the thermal grease the boat worked fine for 5 hrs of time and not it appears my module is bad again same symptoms as before I am going to buy a new module which I should have done before. but other than the grounds does anyone have other things that I should check.

Thanks