Okay, I had to replace my battery the other day because it began to leak acid. Luckily I caught it soon enough, so it didn't do any damage. Before swapping a new one into the engine compartment I removed the battery tray so I could clean it with baking soda and water to neutralize the acid. As I was removing the tray I noticed that there was a vacuum line connected to a small plastic box on the bottom of the tray. I disconnected the line and that released a bunch of air pressure built up in the box. Does anyone know what this box is for? This is the first time I've ever seen one.
1993 ZJ Limited 5.2 - no mods - Red with Gold (what were they thinking) trim.