Check the connections under the handle bar pad, make sure they are plugged in. After that check to see if they are getting voltage, after that check the wire rub through on the harness that runs under neath the engine (do a search on "wire rub"). Then check back
have u messed with the grips lately or put in some bar hooks, because the wires that heat up your hand are in the hand grips and if you cut one of thsoe wires when putting in your bar hooks, the heated grips will either stop working (which happened to me) or get really really hot and melt your glove to the throttle (which happend to me) i went through 2 pairs of hand grips before i realized that i was cutting the wire everytime and that was shorting it out... hope that helps
remember, they are hooked up in series,so if 1 goes bad they both dont work, just plug each grip in 1 at a time and see which one is bad, it may be something else, but I always check this first