Scag mower won't engage

I've got an older Scag 36" WB & went to flip the switch to engage the mower deck this a.m. & nothing happened. The mower itself runs fine (12.5 Hp Kawasaki FB460V), but the deck won't engage. Any ideas where to start w/ the electronics? The walkbehind has been sitting in the shop all winter. Here's a pic to give you an idea of it.