John deer 6400 Shuttle shift will not engauge . I can here a relay activat in the fuse panel. If I hold the lever up the tractor will move forward and the same for reverse. But the lever will not stay there by its self.

You have the old style reverser which has been replaced by one that beeps instead of kicking out.These are a known problem with Deere and that is why you can't buy them anymore.The fact that you can hold it in yourself indicates that the enable solenoid and the forward and reverse solenoid are ok and all safety switches are working.You need to replace the reversrer.