I have a cable comes out of the firewall that is not connected, and have no clue where it should connect? This is located on the driverside of the firewall. Any input would be helpful.
The cable is about 2-2.5 feet long.

 

It could be an addl ground to keep sheet metal grounded or it could supply a ground path for some other component(s). Not knowing all the possible components that are on the vehicle, even a schematic may not take the place of tracing just where the other end of that wire goes. From the pix it looks like a factory job.

There are only so many places a 2-2.5 ft wire can go. If the other end is without any terminal just look for where the terminal might be without a wire connected to it.

 

The one end (on the firewall) is only connected to a screw. I am not sure where the end goes ............maybe to the fender or engine block but the cable is short, confusing.

 

The ground cable from the battery generally goes to the engine block/assy Wire connections from the engine to the sheet metal of the vehicle are necessary and sometimes more than one are used.. I would still look for the terminal eye that might not have a wire connected to it. You would only need to look as far as the wire can reasonably reach.