My 68 S1.5 FHC has the stock plastic glass-mount mirror and I have been trying to install an aftermarket S1 type mirror without success.
I found the three mounting holes under the headliner by using pins (as illustrated) but they don’t appear to be threaded or have captive nuts that I can feel or that will take the screws that came with my S1 mirror. I tried slipping a small metal mounting plate that I had made with the correct threaded holes behind the metal of the cantrail (between the cantrail and the roof from the top) and was able to secure the mirror (screws going through the holes in the mirror base and the unthreaded ones in the cantrail into the threaded plate) , but it vibrated when driving due to the flex of the metal cantrail and I couldn’t see anything.
I was hoping the threaded captive nuts which are supposed to receive the mounting screws were attached to the actual roof panel, but I have not been able to find them there searching blind and haven’t wanted to remove the headliner for a better look.
Its possible that the screws which came with my aftermarket mirror (from one of the usuals) are too small for the holes in the cantrail and this is preventing me from finding the threads. Any idea what size they should be?
Any suggestions from others who have mounted the S1 mirror in an S1.5 or S2 welcome.