If the lock out switch you are referring to is what Kwikee calls a "Step Switch", the fuse is a manufacturers installed fuse. While mine was an add on feature, it was easy to find. If the Tiffin, like my Winnie was included in the engineering of the wire looms, it may be a little harder to find.
There is a RED wire coming out of the four way connector, that should be a wire that goes directly to the battery via a 20 or 25 amp fuse or circuit breaker. There should be a white wire tapped into that red wire that goes to the switch and then continues to the four way connector. There should be a five or six amp fuse in the white wire between the red wire and the switch.
Kwikee Owners Manual #888 has a great drawing of the circuits but does not specify the location of anything added by or connected by the RV mfg.