P0720 on a 1999 3500 ram van

On a long trip, the check engine light came on. I read a P0720 code (Output Speed Sensor Circuit) when at home, then reset it. I think I may have to change the speed sensor on the transmission, which I believe is fairly simple. Can someone help me locate this sensor?

Never mind I found it. since the CEL came right back on It must have been bad. Just went and bought the new sensor and matched it to the bad one on the left lower side of the transmission. A snap to change, but if you do this take care, transmission fluid runs out of the hole. Problem solved. no more CEL.