I'm new to the hobby so excuse any lack of terminology on my part. Is the wire pure black? After looking at mine it looks like it could be one of three wires:
Black with occasional blue dot: goes to left flipper assembly (EOS switch?)
Black with occasional brown stripe: goes to a light
Solid black: goes to unused (on my machine)
If it's solid black, my Creature doesn't use it. It goes to a connector that would plug into slot J1 on the small board on the left, but mine is not connected so I've never touched it. Picture below. Hope this helps.