Malfunction Indicator Light
Any number of reasons... typically it's an error that is detected by the truck's computer system (ECU). These errors can be read by an OBDII code reader (they're pretty cheap on Ebay). Good Luck.
What can I do about it.
Nothing unless you get a code reader, and repair the problem.
Looking for a Used 1500 in your area?
CarGurus has 113,958 nationwide 1500 listings starting at $6,386.
Search Ram 1500 Questions
Ram 1500 Experts