I only found & documented that the dimmer switch rubber cap was only on mustang convertibles as I have only found them on unmolested convertibles & usually low mile cars as that boot can easly pop off dimmer switch over the years. Years ago when I was trying to figure this out I looked up the c5zz part # in mpc & it only mentioned convertible & why # don't have a 76 # in it? I kept finding these rubber caps on restored (non convertible) cars when judjing them & some people think they should be on all cars or an accessory. My thinking on this is the convertible inner rail runs into the torque box floorpan just below the dimmer switch & with the inner convertible rail in the way its hard to find the dimmer switch with your shoe (especially on a manual trans car having the clutch pedal pad in the way) so having the rubber boot on top of dimmer switch makes it wider & easy to catch with your left foot. Just look at how much more room you have in that area between a 4-speed coupe/fastback vs 4-speed convertible. On a coupe /fastback your left foot can lay against the kickpanel but not on a convertible.
