Every John Deere tractor has a model number , look it up on the John Deere website , if you wish , be prepared for a mind boggling list of applications , don't let it overwhelm you - If there is a time element consideration , go inside the cab ,remove the fuse panel cover , usually located behind , or beside , the operator's seat , there is a list in there , of each and every function , in the tractor , check for blown fuses . Next step , go under the tractor , follow the wiring harness , it is usually located on the right side , look up in underneath the cab , check to see if all of the plug ins for the hydrostatic drive are still secured and in place , if yes , then unplug the clips , one at a time , do not mix them up , and see if the drive sensors are ok , or shorted out . Do not remove them , Wendell , unless you have a replacement . If the sensor has failed , and sometimes they do , look to the back of the tractor , depending on your model number , most of them have sensors , on the three point hitch , draft sensing control - you can swap them , from one location to the other , if necessary , to get the tractor home ,and order parts , finally , always check at the back of the tractor , left side , you will find the dipstick for the hydrostatic drive , check to make sure it is full ,they take John Deere hydraulic oil only , do not give it off brand hydraulic oil , they don't like it , make sure the hydraulic oil filter isn't plugged . Last thing , if you have no access to parts , or supplies from John Deere , you can add , sparingly , a small amount of ATF , a good Dexron , SAE 10W equivalent , but no more than one , or two litres , or quarts , depending on the unit of measure where you are . We had one here , a John Deere 6620 4 wheel drive , the operator ran over some tree branches , good size branches , the branch rolled over , underneath the tractor tires , the smaller branches attached to it , caught all three of the plugs , which were attached to the hydrostatic drive transmission . and pulled all three of the plugs out , and what amazed me , Wendell , there wasn't even one broken clip .As soon as the operator , ran over these branches , and the plugs were pulled out , the tractor stopped moving right away , would not move forward , or reverse itself . Good luck Sir , happy hunting , don't let it overwhelm you . The John Deeres are a rugged tractor , they take a lot of punishment , and keep running , but they can also be a real pain in the a** , and give you all sorts of faults , which often have two or three causes for the complaint . Check above the battery box also , where the computer is located , make sure you do not have any corroded , or broken plugs , leading in to the computer . This will also put it in to a no drive condition . Good luck , Wendell , let us know how it turns out .

Roger Rutledge
Technician/Shop Foreman
Green Park Services
Brantford, Ontario, Canada