2003 Expedition traction control problem

Does anyone know exactly where some of these system computers are on this car?
Here's my problem. my Advanctrac system keeps turning off and on by itself, and it beeps every time it does it. To say it is annoying is an understatement! So I took it to a friend that performed a diagnostic test on it, gratis. What the diagnotsics tells us is that is cannot retrieve any data from the traction control computer (I forget if it is the 4wd computer, abs computer, or a seperate computer), and suggest only one of three problems - no power to the computer, no ground, or simply a bad computer. This was all great info, but what he couldn't recall, is where the affected computer was without a schematic, simply because he is an A/C specialist and doesn't mess with the powertrain much.
I am pretty sure it is a bad ground, but I can't do anything about it unless I know where the computer is, or where the ground is. Sure, I could pay the $90 to have them do 10 minutes of work, but the car still runs and drives fine, and I am an aircraft mechanic by trade, so I feel that repairing it myself should not be out of the question, with a little help, please???