The problem is, the aftermarket headlights and fog lamps the previous owner put in, stink. They are so hard to see with at night. I believe the headlights the halos with LEDs built in.
Mustang Parts & Performance - StangMods has an HID kit thats an OEM Non HID to an HID Kit. If the bulb your currently have is the same as factory ones, then this HID kit should plug right in.