Running a sewing machine motor on direct current?
 

I posted about this old Singer 99 motor over here

https://www.quiltingboard.com/vintag...p-t313871.html

And was wondering about the 3 wires coming out of the windings. I think I figured out why there are 3 (but not how the 3 work). I was preparing the cover pieces to paint and noticed on the underside of one of them instructions on converting the motor to run off direct current. Unfortunately part of the instructions are missing so I can't see how to set it up for DC. Two of the wires connect to the brass piece with the "D" and the "A" on it, with only one screw depending on if it's running off AC or DC.

Has anyone heard of running a sewing machine motor on DC? What would that even look like... Did Singer just buy an already existing generic motor and put their tag on it?