I took the throttle assemble off the handle bars while working to install hand guards. After loosening the two phillips screws holding the two halves of the housing together, a black plastic piece fell out and I can't see how it goes back in. There is grease on the side and grease on what seems to be a mating surface inside the front half of the housing, but when I try to fit the front cover back on, the piece binds against the kill switch. Anyone know how this piece fits? Parts diagrams available online only show the assembly together. I have a service manual on the way which must show this thing apart- it has to come apart to change the throttle cable,
Part location found, see second post

 

Ok, I found where it goes and can't believe it. Bike must have been built either Monday morning or late Friday.

This piece fell out of the throttle side housing. Really. Right side where the starter switch and kill switch are located.
After trying for a long time to make it fit, I gave up and reassembled the throttle assembly without it. Seemed to work fine without it.
Then I got to looking at the assembly on the other side, the headlight & turn signal side, and noticed a gap between the housing and the handlebar. I disassembled this housing and my missing piece fit in that gap perfectly!
Before:

After:

What the heck?