the pass rear brake and tail light bulb is noticably dimmer than other one. i cleaned the ground with no improvement. i even cut the ground wire and the bulb still stay lit but of couse dim. where is it getting its ground? again the symptom is same for both filements.

 

by removing the ground it seems as if you have a wire hot wire that grounded itself somewhere between the two sides. If the filiment are running both at 50% with the ground unhooked it is telling me that they are hooked in series. If you hook the ground up does one get brighter and the other go away? Check the cables that one didnt rub and touch ground along the harness.....

 

the brightness of either filament stays same with ground connected. i didn't mention it before, but first thing i had tried was switching bulbs

 

fixed it this morning by replacing socket with new one.