The goof item below may give away important plot points.
When Ponch realizes that Marla is stuck in the car that's hanging from the crane magnet, his first response is to climb the crane and attempt a very daring and, frankly, dangerous rescue. Even if the crane operator has run away, there's no reason to rescue Marla so quickly. As long as they can get her to stay still, someone else can operate the crane and lower the car.
It is never explained way the crane's cable breaks--or how anyone on the scene knows that it is about to break. The car that is hanging from its magnet weighs relatively little, and cranes of this type are built to pick up and carry heavy loads over and over.