2002 dodge durango


abs light, engine light and break lights are all lit. diagnostic error code reads po500 (vehichle speed sensor) I replaced the speed sensor on the rear end. I also want to replace the vehichle speed sensor but I am unable to locate it. Where is it ?? I am also stalling often, my airbag light is on, my air conditioner wont work, speedometer wont register "most " of the time. These things work on and off. Any help is appreciated.