Nighttime tail light not working correctly on driver side - changed bulbs and wiring harness

[AFournier]

When the taillights are on at night (headlights on), they don't illuminate on the driver side. I changed the bulbs out and that didn't work. I figured it must be the wiring harness so I changed that out today. Still not working. The brake lights work just fine. It's the night-time taillights that don't illuminate. I checked the fuse box but didn't see any blown fuses. But if I knew which fuse to change out I would just replace that. Anyone have any ideas which fuse this is, and also what the problem might be if it's not the fuse?

[mikeyk101]

Maybe grab a multimeter and see if there is power to the socket when parking lights are turned on? It seems if one side is working, I wouldn't suspect a fuse. I would be thinking a problem somewhere in wiring to that light, maybe a loose wire at a connector?