Adding a Dimming Rear view mirror to a 95

Hi Has anyone added the option to their car? I have a plain Jane mirror and I wonder if there might be the wiring tucked behind the headliner for the auto dimming/compass mirror. Was it even an option? I assume so cause my 95 Tahoe has it. I hope someone has some good info on this. I suppose I can just run the power wires if need be. No big deal really. Thanks