Did you find the ballast yet? If not you can get a new Dorman ballast from rockauto for $155. I just got 2 tie rods, a wheel bearing and a O2 Sensor from them. Great prices.
http://www.rockauto.com/en/catalog/lincoln,2007,mkz,3.5l+v6,1434491,electrical,hid+headlamp+ballast,15962