Now I know this isn't a Ranger, but I've run out of ideas...

My sister's 2000 expedition lost a taillight a few months ago. I tested for power back to the light and I had power to the pigtail but not the socket. So I replaced the socket. Didn't fix it. She still had the driverside running light, and all the brake and turn signal lights. So this weekend I decided to run a jumper wire from the driverside wire to the passengerside wire. I think I might of back feed the system and fried something. Now I don't have any taillights, no lights on my cluster, and my headlights won't turn off. I ended up disconnecting the battery so it won't run the battery dead. I unpluged the trailer towing harness to see if that made a difference and nothing. All the bulbs are new in the back. Both sockets are new. I couldn't find any blown fuses. Maybe a relay shorted? Headlight switch shot? I'm out of ideas.