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Unfortunatly the horn on the 2008 Ford Escape is in a very odd location. The horn is locaed behind the front bumper below the left front headlamp. The only way to get at the horn is too remove the front bumper.
About the only place you can splice into the wiring would either be off of the interior fuse panel in the cab of the vehicle or possibly the wiring harness that runs behind the left front tire inner splash shield. There is a yellow wire with a red stripe that is the power from the horn pad that you would be looking for. A test light would be best to see if you have the correct wire by pressing the horn and seeing if the light comes on.
My recommendation would be the splash shield as you would not have to run a wire through the interior and outside to the horns.