Where you put the thermostat probe depends on what you're housing your snake in: a tank/terrarium or a tub or a cage. I have mine in racks and they're housed in tubs. I use a single probe and tape it with duct tape (for metal ducts, not the plastic stuff you use to shut up a younger sibling!) in the center tub opening on the rack. Make sure the seal is airtight or as close as possible as you don't want it to overheat. When you say heating pad, what do you mean by that? Is it a human heating pad you get at Walmart or Walgreens? If it isn't a reptile heat mat, buy one of those and ditch the human heat pad. Those get waaaaay too hot and aren't safe for using with a reptile. The thermometer you secure inside the tub or terrarium or if it has a humidity and heat probe, you can use caulk to secure the temperature probe to the bottom of your terrarium and the hygrometer probe (humidity or air moisture content) probe to the side of the terrarium. Make sure the caulk is solid before you put your snake back in the enclosure and the fumes have aired out completely. If you can post pics of what you're working with, that would help to give a better idea of what you're asking and how to help. In the meantime, you might look these over:

This is a good start to look over:
http://ball-pythons.net/forums/showt...s%29-Caresheet

And then one of these two, if you use a tub or a terrarium:

http://ball-pythons.net/forums/showt...e-Basics-*DUW*

http://ball-pythons.net/forums/showt...p-w-pics-*DUW*