I bought a new Carlite windshield for my 68. Like all 68 - and up Mustangs / Cougars the mirror button glues to the windshield. I started out by laying out where the center of the windshield is, and attempted to place a piece of masking tape there to make a mark. The masking tape would not stick! I cleaned it first with lacquer thinner. No good, tape still would not stick. Then I tried Goof Off. Better results, now tape will stick. I used the Goof off to clean the area where the mirror button goes, because tape would not stick there either. Finally it - whatever the residue was - seemed to be gone. I followed the directions on the windshield mirror adhesive, using the primer / activator first, then waiting 60 seconds, applying one drop of adhesive to the button, and holding it in place for another 60 seconds.
All seemed good. I waited until the next day and installed the rear view mirror.
Two days later I am working in the garage and I hear a clunk inside the car. The mirror was laying on the console, undamaged thankfully. The windshield had no signs of adhesive remaining. The mirror button has the adhesive stuck to it.
Anyone else had this problem? What fixed it? I am out of ideas.