Auto dimming/compass mirror pinouts

I have the rear view mirror #GNTK-851 in my SR5 which has the auto dimming/compass. I also have an unbranded mirror with homelink I was considering switching out. I have the pinouts on the unbranded so I can easily see the Batt, IGN+, Ground, and it even has reverse (though I don't know why).

It looks like Gentexk does not publish their pinouts. I was hunting for them here (and the great and powerful google) but could not get a clear lead on the wiring of the 851. I put a put a meter on the pins for the 3-wires. I get the Batt (blue pin4) and IGN+ (brown) so I suspect the GND is the white/brown. If I can be sure I am considering swapping them out. I'd have to tap the wires but meh, my truck. Would any of you caution against this mod?

I see where I can by a new homelink mirror but if I don't need to spend the $150 on it I can use that cash elsewhere...like my OVTune fund!

 

This may help.