It is within the pedal. I suggest using this diagram at the link. It's got a picture, and step by step instructions. (BTW, it looks pretty simple) http://www.explorerforum.com/forums//showthread.php?t=146986

Everyone I've ever done has been between the pedal and the rod that comes through the firewall from the master cylinder. It isn't hard to do at all, except that you have to do it lying on your back under the dashboard with your feet hanging out the door. It is a LOT easier if you pull the driver's side seat out first, which, incidently, is just four bolts. If I remember correctly, it takes a half inch socket. Do the two in front of the seat, then fold the seat forward or run in forward and do the two behind the seat. Then lift it up and out. Make sure you don't change the seat adjustment while its out of the truck or you will have a heck of a time getting it back in. Reinstall is the same procedure in reverse, just make sure you get the bolts back in tight. With the seat out of the way, lie on your back under the dash. You should see a pin through the brake pedal. If I remember correctly, it has a cotter key on one end. Pull the key and the pin and the rod that comes through the the fire wall should drop free of the pedal. The switch will be nestled into the joint between that rod and the pedal. As I recall, the joint itself is all that holds it in there. You should be able to just pull it out and set the new one in there. Then reassemble the joint and the pin and pop the cotter key in. Then extract yourself from that tight quarters and reinstall the seat.

in the brake pedal linkage