700 C John Deere Dozer

Good evening Guys I have a customer that has a 700 C a lot of mechanics even John Deere Field service has been working on this unit but know one has repaired it when I checked it out I found the speed selector switch on the left joy stick was shorted and all the wiring was stripped back any way I changed it out today and at first I got a F675 code I let the unit run and warm up to operating temp. the code went away still no travel fwd or reverse when you shut the unit down and crank it up it jerks fwd then reverse and then stops moving still no codes for about 1 hour then all the sudden the alternator light came on I checked the alternator and it is charging 28.7 volts at the battery and the alternator then the code came back f675