Reverse light voltage in Compass/Temp Mirror

[ndav8r]

Hi Gang!
A while back I started a thread on wiring a Compass/Temp rear view mirror in my 02 Sliverado. After discovering in the headliner a factory harness for it, I aquired a mirror from an 04 Silvy. With schematics from both years, I was able to convert from the 7 pin to the 16 pin connector with no problem. Works great!
Now my buddy who owns a very nice '94 Silverado has a 04 mirror to install in his. In his case I have to wire from scratch...ground, 12v+, both sensor leads, and reverse 12v lead.
My question is this::: What is the reason for the 12volt lead from the reverse lights? My mirror shows temp and compass even before I shift from Park. Do I even need this lead?
Thanks.
NDAV8R

[2000CAYukon]

I think the +12 reverse voltage is for the auto dimming feature. In reverse, the auto dimming is turned off.

Again, not 100% sure.

//2000CAYukon

[vnotaro]

Auto dimming is turned off when you shift into reverse.