What are these holes in my Suburban door for?

[derail]

Originally Posted by rbar

Mine doesn't have any mirror mounting spots on the passenger side either. I am thinking about using nutserts for that instead of trying to put nuts on the back side.

That's the exact same thing I used on my passenger door and it worked awesome! If you can look inside of the door, I think most of the passenger doors have the backing plate already in the correct position with holes pre-drilled.