Aren't there supposed to be two wires connecting to the battery holder

I am trying to repair a Chantilly Singing Bear. The batteries were corroded inside the battery holder, so I cleaned it out with baking soda, but still it doesn't work. Opened it up and noticed on the red wire is attached to the battery holder, and there is a loose black wire just dangling from the circuit board not connected to anything. Isn't there supposed to be both a red and black wire connecting to it? Also, general tips on how to connect the wire back would be appreciated. I am very new to this.