2003 Montero Sport brake/tail light

[UtahVet]

I've got a 2003 Montero Sport with a tail light issue. The driver side brake light wasn't working, but the tail light was. I replaced the bulb, and the problem persisted. Next I checked the wiring, all appeared to be well. I then cleaned off the socket with electrical parts cleaner and adjusted the two points to better make contact with the installed bulb. Now I have a working drivers side brake light, but the tail light function no longer works. I'm not sure if it is the socket itself, the wires coming out of it, the connection between those wires and the main ones or the main wires that run through the vehicle. Any advice would be much appreciated.