The Reverse Inhibit input at Pin 3 is used to prevent dimming when the car is in reverse. An example for this is when a vehicle is being backed out of a garage. In this situation, the mirror would normally dim as the forward light sensor is dark and the rearward looking sensor is illuminated. The standard harness does not include wiring for this function. To remove your new mirror, simply slide a narrow screwdriver up between the button and the spring clip on the mount, that will then allow the mirror to slide up and off the button.
Installation is now complete.
Enjoy your new mirror.