[Gerry Zagorski]

Yep - My guess would be a ground wire as well. Looks to me like the terminal lug at the end has corroded away.. There should be a circle at the end were a bolt goes through and the bolt screws into a metal part of the engine to provide a ground.

Looks like you have a hole with nothing in it and that is perhaps where the terminal lug is supposed to be bolted to and the bolt is missing as well...

If that is the case you will need to crimp a new terminal lug on, find a screw to fit that empty hole and mistery solved.

If it turns out that the empty hole I'm reffering to is not a bolt hole, that wire had to lead somewhere so I would simply see where you can stretch that wire to, to find out what it was attached to.