1994 Chevy S-10 Electrical....starter, closed fuse?

After replacing water pump and battery three weeks ago....heater quit heating and noticed a leak in the water pump and that the positive battery plug had snapped, I went to start my blazer yesterday and the motor kept cranking loudly like a belt being stuck. Tried to shut off the ignition and even with the key out, would not shut off. Finally disconnected the negative battery cable and it stopped. Thought it was a bad ignition switch and replaced that (boy what a job that was) only to have the same problem when attaching the negative cable back on the battery, the car wants to turn over again....without the key. fuse, circuit, cable???
Any help would be greatly appreciated.
Richard Craig