Re: Problem with my ford escort 88 battery or alternator?
The other end of the - negative battery cable is connected to the engine. There should be a ground strap from the engine to the body to transfer the ground to the body, but sometimes can be broke or missing and that's why there is a smaller wire coming off the cable that connects to the body to ensure a proper ground. In other words, you may not be getting a good ground to the body from the engine. That's why the smaller wire needs to be connected. If you can connect the small wire anywhere to the body that is metal it should be a sufficient ground to the body. If it does not correct your issues it you may have wiring problems elsewhere in the electrical system.
A socket of the correct size or even a crescent wrench should remove the bolt. After removing the bolt, slide the eye of the connector over the bolt and reattach. If its the bolt shown to the right of the battery in the photo that you're talking about, it looks like a 10mm to me.