I'd also like to say thank you for the solution here. Since I knew install.php no longer existed, I figured the redirect must have been hard coded. I soon found the redirect in main.php but it appeared to be because there was no database connection. I checked and re-checked that and I didn't understand why ?flush=1 and asking for other pages worked, but not the home page. I ended up finding this forum post about page 4 of a search for install.php. Just to make it easier for someone else who may need this post I will add some other terms here that will come up on searching the forums.
Redirect to the installer if no database is selected.
Redirect to install.php
main.php redirects to install.php