The weather was fairly nice today so I did a little snooping and found the horn. It's located in front of the driver's side front wheel. I drove it up on ramps and pulled of the first three clips holding the front lower fender liner on. There is a 10mm bolt holding the bracket onto the body. The harness kit included in the package with the replacement part I got from my local GM dealer did not include the proper connector so I just removed the one from the old (water-filled) horn.