I'd be surprised on that age car if it wasn't plug and play, ie ford left a socket there for towbar leckies to be simply plugged into, I'd be tempted to investigate this first, lot less hassle.
I don't know the wire colours on your car, but even if I were given the colours it would be best to double check, ford do like to change things, with that being the case if noe asy plug solution metre would be your best mate, also do you have any bulb failure warning in the car, if you do will need a bypass relay to prevent the lights showing when towing.
tabetha