I have the same problem with my wife's Tarus, only it's the passenger side. Most likely it's your switch, not the wiring. Here's what you do to check it.
Take the switch out and disconnect the quick disconnect wiring chumpy (tech term there). Get a battery charger and plug it in. Use two small wires (one for negative, one for positive) and stick them in the battery charger clamps. Now, stick the ends of the wires in the holes of the wiring connector thingy (another tech term). I believe it's positive to positive (or negative to negative) will put the window down, and negative to positive wil put it up. If the window works by doing this it's your switch. That is what's wrong with the wife's car, but nobody sells the switch. If it doesn't work then it's probably the wiring.
Although I've done this several times with great success I cannot be held liable for any, um, "complications" you may run into.
