I just wanted to put this out in an easily located format, so anyone else installing a 4th gen rear view mirror would have an easier time of wiring the maps lights up.

On the 4th gen mirror, there are 3 wires, orange, black, and brown(tan). Black is the ground, orange is 12v hot, and the brown wire is the switched ground. The way I connected mine was run all three wires to the dome light area. This is in an 86 Camaro.

Orange from mirror connects to the white/orange wire to the dome light.
Brown(tan) from mirror connects to the white wire from the dome light.
Black connects to ground.

On mine, I had the overhead map lights on the dome light that didn't work, so I was able to connect my orange and black to the wires that originally powered the map lights.

The white wire from the dome light, is the switched ground. It has 12v on it when the doors are closed, dropping to 0v when you open a door and the door switch grounds the line. The map lights on the mirror will then function normally, able to be turned on via the switches on the mirror, and coming on automatically when you open the doors.

I hope this helps.