Wheelchair Seat Belts 1994 Nissan Sentra,battery Accidently Connected Backwards?

1994 Nissan Sentra,battery accidently connected backwards? - wheelchair seat belts

My aunt's husband who is in a wheelchair, you change the battery in your car and crossed the borders of cause enough.Said could not see the connections on the hot wire near the battery smoked. Now the work begins and the lights of cars, but none of the CWC. Work. Turn signals, radio, tensioner seat belts ... etc. Where was the first place to look for the problem.