The seat is awkward and heavy. It would be easier to install the bench and attach the motors if the backrest could be installed separately. I didn't want to risk damaging the backrest by prying on it. I've also read that you have to be careful with the backrest wings. A 1000 thanks to anyone who can provide photos/detailed instructions for separating the bench and backrest.
The back of the seat is held on by two pegs (one on each side located on the bottom. To remove the back, the seat back must be stretched out to clear one side. I have done this this way. get a belt (the kind that holds your pants up). Snake it around the dogleg at the bottom of the seat back and pull so it clears the peg. Might be better to have a helper - one person to pull, the other to move the seat back away from the peg. Reinstall the same way, but the helper has to line up the hole with the peg
Note - now that I have written this, not sure which part has the peg, but instructions remain the same.