bumper mounted towing ball

This is probably a stupid problem/question but I recently noticed that on my 1999 blazer there is a place to put a ball for towing a light trailer, the only problem is that I can't figure out how to remove the plastic cover that covers the hole and the threads where the ball goes. Also I was wondering if it comes with a wiring harness or am I going to have to go out and buy one.

ok, i am going to tell you how i did it, not so sure this is the 'right way'.  i took a utility knife and carefully cut into the plastic cover over the hole.  it is roughly a square in shape and approx. 2" in size.  this exposes a bit of the bumper so the ball's shoulder will contact the metal of the bumper and not the plastic.  i feel that cutting away the plastic from just the hole would not allow a proper tightening of the ball.
 
i have a '00 blazer, so there is a good chance yours is similar.  the wiring is just to the left of the tag, behind the bumper, wire tied to a crossmember.  you will need to buy a 'kit' that allows you to splice ito the vehicle's wiring.  make sure you get a plug that matches your trailer's.
 
the hitch ball proved to be too high for my trailer.  i eventually bought a receiver hitch that allowed me to drop the ball a total of about four inches.  this allowed my trailer to be towed pretty much level.  installing the receiver hitch was painless.  i did have trouble removing the original bumper bolts which were a bit corroded and the access was not so easy.