why would condensation occur on the inside of my tail light?”
Simple. Those no-touch car washes hit your car with streams of water that go through the nozzle at 1500 PSI! When I use one of these, my car rocks back and forth! You probably have a very small crack or a slightly loose gasket on that taillight. They have gaskets because metal contracts at a very different rate than plastics, and the flexible gasket is supposed to make up the difference. But in really cold weather and when hit by a fast stream of water, stuff can get past the gasket. Id open up the modesty panel behind the light and unscrew the light sockets and leave it open overnight to dry out. And maybe run a bead of clear silicone caulking around the taillight to metal joint. Wipe off the excess with your finger. The wipe off your finger on a paper towel.
