Problems with melted tail light bulbs on 1999 Ford Windstar

I keep having to replace the drivers side tail/brake light bulb, not because it burns out, but because the base keeps melting around one of the contact wires.
Anyone have any ideas why it keeps doing this?
Oh, the bulbs I'm using are Sylvania 3157K

Asked by for the 1999 Ford Windstar
It sounds like a resistance problem in the socket. If the resistance is too high, then there is more current drawn in order to light the bulb which creates heat and it eventually melts. What does the socket look like? Is it corroded, green and funky or is it clean? if the socket isn't really clean, they are not very hard to replace and not very expensive. You can get one at a parts store and install it your self. Usually the crush style connectors work decently for light circuts.

I would suspect the socket. Does it melt on the other side? How are the connections from the socket upstream. How good is the ground connection. Is it loose?
The socket is blackened from the heat generated, other than that there is no corrosion on the contacts in the socket. Each time I replace the bulb I scrape off any discoloration there may be on the contacts.