The upgraded wiring harness is required for ALL headlights on the Taurus/Sable from 1996 on, if you want to maximize output. Do yourself a favor and take a look at the stock wiring. It's pitiful... I kid you not, my dad's lawnmower has more substantial headlight wiring on it.
The upgraded wiring harness consists of heavier-gauge wire, new sockets (to plug into the existing wiring) and relays to switch the current into the new wiring. Basically, it's plug and play, plus a connection at the battery. Since you are using a relay circuit, the old wiring only has to power the relay so that the lights are switched with the stock headlight system. The actual power comes straight from the battery through the upgraded wiring harness to the bulbs.
Here is one example of this system. There are other sources, including eBay, where I saw a set for $27 the other day. Of course, that was direct from Taiwan, and it had Chinese relays
, so I would avoid them for long term use--but that's just me. *EDIT* Hmm... the ones in that link look Chinese too. Oh well, you can always get some Bosch relays at Pep Boys and swap 'em.