I have a 2005 1500 when the truck is started you can push the cruise button and the light come on. However going above 10mph the light goes off and will not come on while driving. Really want to fix it cause I hear it's better for gas mileage.

 

Speed control sensor is bad,

 

How and where can I find the sensor to change it?

 

Depending on what model you have, my 04 has 4 wheel brake calipers and the speed control sensor is on the front left wheel hub. You will find a wire coming out the back of the hub and going up into the engine compartment. Could be the sensor is just dirty.