Marsha, You do indeed have a 15-91. Go to this page:
http://www.singerco.com/accessories/...manuals/search
and you are able to download a PDF file for free of the manual for this machine.
I've never seen one wired like yours. Interesting! It looks tho, like you could if desired, unplug the motor control from the machine and plug in a regular foot feed/power cord if you wanted. (You can get it from Sew Classic) I, personally, wouldn't. I like the kneebar myself, and you have a nice cabinet to leave the machine in....
Tell your spousal unit that he did good!!