Additional info on Post #729.
After additional checking with meter, I found the smaller (yellow) wire was getting 4.5 VDC off the window and sending that back to the switch (assume for illumination when on). Additional wiring diagrams indicated a resistor (unknown value) or may have just been the heating grid itself, but window was getting 12-14VDC in and only 4.25VDC out.
Found a 12VDC to 6VDC pwr converter on Amazon for $6.78.
Installed today and still have mirror heat & switch illuminates when on. Left on till it timed out (15 minutes). Converter was cool to the touch. As installed is completely out of sight & all plug in.
Although I experienced no ill effects from original wiring described, I felt it was safer to send 6VDC to the switch instead of 12VDC when the OEM sent 4-5VDC.
This is for info ONLY and is on a 2013 5.0 Lariat. No warranty expressed or implied. If you attempt, your results may/may not be the same.

 

For those with the failure, is it the drivers side glass that shatters?

 

Mine was indeed the driver's side. The passenger and sliding windows were not affected. Of course it's all one big assembly, so the whole thing needed to be replaced.

 

I understand. My hypothesis is that the defect causes the drivers side to break. So I'd like to hear from those here who have actually had the glass break.

 

My passenger side shattered.

 

Mine was the passengers side of the glass that shattered.

 

Mine was the passenger side.

 

I have a feeling it's gonna be like water and the path of least resistance. whichever side has the flaw will break.

 

I was speculating that the contact area was heating up more than the rest due to a bad connection and causing the breakage. But that is confounded by the facts.

 

Since ground wire is on driver side, would lower gauge (larger wire) for the ground cause less resistance, slower and less heat build up?