Original/Stock Self-Dimming Rear-View Mirror fell apart.

I purchased a new **** Dimming Rear-View Mirror.

How should I wire the new rear-view mirror?

According to the directions for the new mirror, I am to attach it's harness by 2 wires.

The 2 wires are: 1.) ground wire & 2.) 12-volt wire to an ignition controlled wire (power source)

The Original/Stock Self-Dimming Rear-View Mirror's harness has 3 wires.
The wires are the following:
1.) Purple
2.) Blue White
3.) Black

Can anyone tell me which of the stock wires would serve as the ignition controlled wire (power source) and which of the stock wires would serve as the ground wire?

 

This is for a 1998 Dodge Ram 1500 SST

 

Moving this to the tech forum.