So I bought some carpet off a vender on eBay it's for a bronco... it doesn't seem to be cut exactly to the body.
By that do you mean that it's got extra material you'll need to cut off? Or are there spots that don't contour exactly to your body?
If the latter, perhaps the body has been modified.
Question is the high beam light switch mounted under carpet normally or is it mounted on top of the carpet?
Neither. It's "through" the carpet, meaning that the switch remains bolted to the floor panel, but you have to cut the carpet exactly over the switch so that it peeks through. Most kits come with a plastic ring/grommet to clean up the cut hole, protect the carpet edge from fraying, and to make it look neater and more professional.
Not sure where best to get the glue, but the old 3M "77" stuff is available at many places, from auto part stores to likely Home Depot.
Paul