Welcome to the form and irv2.
Below in my signature you will find links to many items for your Newmar.
Here
is one for fusing that should help.
You will find step information in
QT's # 3 link.
Workhorse Forum LINK
You may have a panel on your dash where some fuses maybe located also.
You trouble may not be a fuse but a wire connection from the door switch to the chassis frame for ground for door switch. The connection can become corroded and cause your problem.
You will have three ground wires for step a heavy green wire to chassis frame, a short wire from control to one of its mounting screw and the door switch wire to frame.
When ever your working on step keep your body out from under steps if you get caught.
Enjoy the forum and saft travels.