I need a new battery cable, Where does the battery cable disconnect from the engine?

Which cable? Can't you just follow it to where it's bolted on? Depending on the starter system used, the larger red positive cable will bolt to the solenoid on the fender or right to the starter motor under the engine. If it's bolted to the solenoid, another fat cable will go from the other large terminal on the solenoid to the starter. That one causes a lot of trouble from corrosion occurring under the insulation where it can't be seen.

The black negative cable has a small wire that bolts to the body, usually one of the fender bolts.