Originally Posted by manofmany
It was vice versa before I swapped a new bulb in. My tail light on the drivers side will not illuminate but the brake light will. What in the world could that be? The socket maybe? Can I get just a new socket somewhere?
The reason for this is that the bulb socket is rotated 180 degrees out of position. The contact points need to be properly aligned (notice there are two contacts on one side and one just one contact on the other side). In the picture below you can see the two silver contact points on one side. The other side (behind and out of view in the picture) has just one:
The bulb unit (a twist in twist out circular unit with a fin that has a notch on one side of the top of the fin cut away) has three contact points for the dual running-light and brake-light circuit. Notice the notch on the bottom left in front of his thumb.
If you look at the lens socket into which the bulb unit is twisted, you'll see it also has three contact points (one on one side and two on the other side).
A common mistake is to insert the bulb unit the wrong way in (rotated 180 degrees). The side with the two contacts on the bulb unit has to line up with side on the lens socket's seat with the two contact points. Likewise the bulb unit side with just one contact point has to line up with the side on the lens socket's seat with just one contact.
You should have three bulbs in each tail light. The two bottom lights will have the fin-notch on the upper side I believe. The fin-notch on the inserted bulb socket for the top light (that contains the combination running-light and brake-light) will face the opposite direction from the two bottom bulb sockets.