96 chevy 2500 heavy duty won't start when it rains

What is your question?

Please forgive a seemingly stupid question. I am a grandmother and not mechanically inclined. My truck would not start when it is high humidity. It turns over but won't catch and when I turn off the key almost starts an then shudders with a loud clang in the motor. A retired mechanic told me a few years ago it was a module that needed replacing. I picked it up and took it to a friend to be installed. He did not believe that the module was a problem and showed me he had loosely installed it but left the old one hanging ( Between the carb and the firewall) so I could return the new part if it made no difference. It worked like a charm until a few years later when they both fell off. I want to pick up a new module but can't remember what it was called. Does anyone know what that module is?

What makes this problem better or worse?

high humidity

How long has your 1996 Chevrolet C2500 had this problem?

a couple of years