Can't get rear brake light to stick to window
 

I've got a fantastic brake light all wired up for my '79 Targa SC. Unfortunately, nothing I've tried can make it stick to the window.

I tried super-glue, double-sided 3M tape, and JB weld epoxy.
The super-glue never held at all, maybe it doesn't like glass-to-plastic?
The tape got warm in the sun and the adhesive released.
The epoxy held on until I tried to remove the tape I used to keep it in place while it set.

Any ideas?

Doesn't sound like you cleaned very well or didn't let the cleaner dry enough before installing.

Remove whatever is there now, with a flat razor blade. Clean with rubbing alcohol thoroughly. Let air dry 5 minutes before you use any clean cloth to also wipe dry.

Use the 3M clear glass/mirror double sided tape. Excellent for this application. I used it to hold a 8' plate mirror onto a custom stainless steel metal frame and could not get it loose.

If you are ok to pay the Porsche tax, you could order the adhesive from the dealer part number A 000 043 069 00 adhesive for frame for light

Any 3m doublestick will secure it for years. Installed mine in 2008. Sounds like there's silicon or something on the glass.

Acetone, then alcohol should get the grunge off.

How about the little tube of adhesive that bonds your rear view mirror "puck" to the windshield. Just takes a tiny drop. All the FLAPS have it. It bonds the mirror like crazy!
Just a thought.

When I re-did my tint, I used clear 3M glass tape, worked perfectly.

As the 2 posts above. You need to use the stuff that is designed for this application.