I'm confused as to why your A&P is "advising" you to replace parts, but at this point having followed the entire previous thread and made a good faith effort to give you some information to trouble shoot with, my conclusion is that you're massively out of your depth and it's only going to be by a stroke of luck that you stumble across a solution.
Get your A&P, or a better one, out to your plane and just have them fix it. This is a very simple problem and would take someone who knows how to actually use a voltmeter less than 10 minutes to diagnose.
