What's the little button for?

What's the little button for ? drivers side on lower dash next to motor cover ? I dont have a manual when I first bought it a few weeks ago it had a little green light on, and if I pushed it , it would change to red? overdrive? its 02 Ram van 1500 V6 thanx :p

I have one of those buttons in my van, and it's for turning off the overdrive. It's set to overdrive on my default when you start the van.