I haven't done one in a couple of years but I never had an install on this not work. I have done scores of them.
Tape on the outside of the windshield where you want the tab.
Clean the inside of the windshield where you want the tab.
Clean the new tab.
Spray/wipe primer on windshield where you want the tab and put primer on tab as well, on the side to be bonded.
Let primer dry.
Put one drop of adhesive on the tab.
Press tab on windshield under tape that you put on the outside. Do not, twist or wiggle and hold tight in place with your hand for 2 minutes.
Let go and let it dry another 2-3 minutes and put the mirror on.
Don't yank or fuss too much with the mirror until it sets overnight.
Never had one fail yet.
I use to do so many I had a larger kit of glue and primer but now just use the one job Permatex Kit or Loctite kit that NAPA sells.
Maybe the stuff has changed.