Hi,
I have a 56 STTDCI, I used the Ford wiring kit, it just plugs in to all the right places, has all the necessary relays and sockets. It is not cheap, but for a painless installation you can't beat it, it took me about 1 hour to fit, hooked up the 'van everything worked perfectly. I have fitted towbars on the last 20 or so cars I have had, this was the least hassle by far. A word of caution though, I had another Mondeo, a 55 plate, due to me being away on business, my good lady wife had someone come a fit the towbar, they "scotch-locked" the necessary connections in, but it never seemed to work as well (dimming lights etc.,) as my present Mondy does. I have been a Automotive Engineer for years and hate "scotch locks", though some people swear by them. I would always use the correct gear for doing anything like this, not the cheapest I agree, but a better installation and as I have said, least hassle by far.
Good Luck.