Read carefully what Dave571 posted, and test it this way: Turn off ALL loads, radio, and any solid state (stereo) loads, lights, etc.

Run the car at a good high fast idle, and flip the disconnect off

The car should stop running. If not, you need to change the alternator wiring. There are several ways to do so, but probably the simplest is to run TWO hots to the trunk, a #6 or so from the alternator to the battery, or you can run an extra relay to kill the alternator, or you can buy a 4 post switch and put the small posts in the regulator supply lead.

This is very important. If you should wreck with the engine running for some reason, you want to be able to kill everything