If you don't hook up pins 6 and 7 you won't have a temperature display at all. As Zebrafive said pins 1 and 2 are switched power and ground, pin 3 is reverse signal(to kill autodimming when backing up as a safety feature), pins 4 and 5 are unused but actually go to the outside mirrors when they are equipped with auto dimming feature, and pins 6 and 7 go to the temperature sender which is specific to the mirror, which is different than the temp sender for the Blazer/Bravada overhead console even though they look alike and have the same connector on them. As you can see there is NO speed signal wire that goes to the mirror and will update the display every few seconds. The wire colors may vary depending on the vehicle the mirror came out of but the order will be the same with pin 1 being located towards the passenger side of the vehicle and pin 7 being located near the center of the mirror.
However as mentioned above in the Blazer/Bravada overhead console it does have a speed sensor input which controls the update speed of the display when the temperature goes up(to prevent erroneous readings caused by the car not moving as the temp sender is located near the radiator). - Peter
1995 Caprice SS/9C1 Black w/ tan leather interior
1993 Ford Escort LX Mocha Frost Metallic w/ tan interior