Tail/Brake Lamp

I have a 1991 Ford Escort Wagon.
The drivers side Tail and Brake light bulb burns out frequently. Were do I start to figure out the cause? I have had moisture in the tail light assembly when I have changed the bulb.
Any Thoughts?

It's definitely the moisture that is causing the problem. Take the lens apart from the backing plate and let it dry out real good. Or, if you can get an electric hair dryer you can dry it out where the bulb assembly goes it. Then get a tube of silicon sealer and seal it real good wherever moisture might get into it. Where the bulb goes in and where
the lens goes on. I've had the same problem. I don't know why moisture does that. Anybody out there?

I would take the tail light assembly off. Duct tape the holes where the bulbs go and then put it under water to see where your hole is at. This might be happening when you wash your car.