1997 Mercury Grand Marquis Owner Guide 1st Printing - Page 102

The electronic mirror measures the brightness of the light coming in from the rear of the vehicle. It automatically makes a correction in the glare state. The mirror may be turned off in either the normal or non-glare position. There are two light sensors (photocells) in this mirror. The sensor that detects rear glare is located inside a window in the center of the mirror. The second light sensor which determines outside light level is located on the backside of the mirror case. NOTE: Do not block the sensor on the backside of the mirror (i.e., with a parking tag, car deodorizer, etc.) since this may impair proper mirror performance. One important safety feature is that the mirror automatically returns to the normal position whenever the vehicle is placed in R (Reverse) (when the mirror is in the ON position). This feature ensures a bright clear view in the mirror when backing up. 101