Yup...here's the quick fix...

Take the bulb out of the socket. The metal edges and prongs that touch the other metal connectors on the taillight assembly are corroded a little. The current is getting there, but its not registering.

On the bulb socket with the metal prongs and metal edges.. Use a little sand paper and sand off the corrsion a little bit....do it as you go, and the bulb should fire up again. When you put the bulb back in and put the gizmo that holds the bulb back into the talil light assembly, move it around a little bit and keep the lights on so you can see when it fires up. I do this every couple of months...