Left side tail lights don't work
 

2005 S60. Right side tail lights and all other lights (brake, fog,etc) at rear work. The 2 left side running lights don't work. Bulbs good, bulb assembly works fine when I plug it in on right side. Both sets of tail lights on same fuse so that is ok. I dropped the fuse box in trunk and disconnected plug in back. When I start to reinstall the plug, the left side lights come on for a second, then there is a click that sounds like it comes from in the fuse box, and the lights go out. I can do this over and over with the same result.
That fuse box looks like a bear to try and open so I have not tried that yet. Am I missing something or is there something in that box that is causing the problem? And if so, what's in there, and can I get at it?

2005 XC90. Same issue but on left side. Both running lights in front and back do not work. Changed bulbs, cleaned out connections. Nothing. Right side works fine. Been having lots of bulbs go down lately too.