Any chance you could re-post this diagram at a higher resolution (I.e., larger) so that it is legible? Thanks!

 

It could be a loose wire or other connection, but it’s very probably the relevant contact in the driver/passenger selector switch. I was able to disassemble the switch assembly and clean the contacts in an ‘08 LS.

 

Here's a different schematic. Maybe it will help.
(red wire cut off at top, goes to the mirrors fuse)

 

We all have our theories on this switch/mirror problem. Let me just add mine. I have purchased and replaced 2 switches in my '07 LT. each time the switch works fine and the mirrors work fine. I have taken the old switch apart tried to clean the contacts with no luck. I personally think it's a cheap lousy switch.
Beachbum1