Many brands have a manual crank and an access hole located on the opposite side of the trailer. But even before that, if you don't hear any motor noise when using the switch, then there is an electrical problem, motor, fuse, switch or loose wire. On most units, the transfer tube between the two racks is next to the frame and clearly visible, not hidden in the underbelly. Some times one side may jump a tooth or two and get out of sync. Also, the tube has a sheer pin to prevent serious damage.
Larry Day, Texas Baptist Men volunteer
'13 Silverado LT 3500HD D/A CCSB 2wd, custom RKI bed
'11 Crossroads Cruiser 32MK loaded