Hello Gary,
That’s a good question. The P55 motor was only around for 3 short years. 1948 to 1950. The Girders and Gears website has a complete history of the erector motor.
History of the Gilbert Erector Motor
That’s a pretty rare motor you have. It was only produced for the top-of-the-line No 12 1/2 sets. That’s a nice set to have.
There is no book or video on hooking it up. Best thing to do would be to get the manual that came with the set. It’s possible one might come up on eBay or even a reproduction one.
I hope that at least gets you headed in the right direction.