Hello fellow Michigander!
Plug the heater in. Let the engine cool down, like overnight.
Take off one glove long enough to place your hand on the block near the heater. If it's working you should have a warm, and oily, hand . If the heater isn't working, you will probably have a cold, oily hand
It's really cold here, but the oil should keep your hand from freezing to the block if the heater isn't working.