I'm scratching my head on this one. My previous owner installed an Alpine headunit/Amp. I had that
ripped out and converted back to stock.

The issue is that I get no sound through the main large speakers on the door and only comes out of the tweeters. Even then
the tweeters are sounding extremely low and faint. It was working for a bit after the conversion however no longer the case.

I pulled the head unit and made sure everything is tight in the back however unsure what else to look at. Any ideas?

Thanks

 

The factory speaker wires run into the doors, and then split to power both the woofers and
the tweeters. If you are getting sound to the tweeters, then the problem is in the doors.
You don't mention how the amp was hooked up to the door speakers, but perhaps the
previous owner ran separate speaker wires from the amp into the doors, though it's a little
strange he would only power the woofers off of it.
It's not particularly difficult to remove the inner door panels to figure out what is going on.
This site may help.