Odd sequencial issue

Right side works fine, sequence, brake, running OK
Left side has brake, running but no sequence until I pull the outer bulb socket. Once I pulled the outer bulb socket, the middle and inner sequence? Any suggestions? I cleaned the ground by the filler neck.

When I have an issue, I refer to this:

http://www.thuntek.net/cougars_unlimited/#Sequential_Trouble_shoot

Sand socket and hole in which it is inserted and use a new bulb… all you may loose is a bulb that can be kept as a spare anyway. If that does not work, check that he wire connection with that socket is good an thight.