If you are going to run a amplifier where you need a 140 amp alternator, you aren't going to be running power through the dashboard connections, so much of what is written about that subject just isn't going to apply.
Thank big John I'll take a look when I get a chance
So, 140 amp alternator? That would tell me you are thinking of a 1200 watt system? If you aren't getting into that much wattage, you don't need an alternator with that much output.
Even with a smaller amplifier, you are going to want to run a separate wire from a battery source to your amplifier and not tap power from under the dash (which again, eliminates all the nonsense about how much current is running through the dash)
I would do this mod first:
Underhood Ammeter Bypass That will bypass the dash wiring/ammeter/bulkhead connector for charging current. The thing you need to remember is your alternator will only put out as much as it needs, so everything is more dependent on how much you use rather than how much you can charge.
There is sooooooo much BS, nonsense and misinformation out there... People will lead you down a path of insanity if you aren't careful.