Left tail light flickers, need help?

My left tail light, the light on the trunk, it is either on, off, or flickers, I have no dash warning light, if I tap the light it either goes off, on, or flickers, which makes me think it might just be a shorted wire, the light is still bright and works fine when lit, I saw a bulletin for the rear tail lights, but I believe that is for the outer taillight which flickers due to corrosion, thanks for any help...:confused2