Power Glide Wont Backup when hitting button or switch at times any ideas has probrake

Is this an intermittent problem? Or every time? If intermittent, I would be looking at the electronic side of things. Switch,solenoid, wireing, etc.

intermittent switch and wiring is new and it did it before new wiring ......

wrong solenoid. Most are .200 throw. Some use and need a .220 throw.