You may want to buy a new post clamp. I believe its much safer this way.

How To Disconnect A Car Battery 5 Steps With Pictures
Battery disconnect switch installation positive or negative. Wife 16 year old son 7 year old son and a black lab dog. To be nhra legal first you need to mount the battery in a sealed box that has a vent exiting the outside of the car. Assuming a negative ground car disconnect the existing wire from the battery negative post and remove the post clamp from the wire. Disconnect the negative terminal usually black marked with a sign. You also need to run the altenator charge wire to the battery side of the switch or directly to the positive terminal of the battery. Theres considerable controversy over whether its best to hook up the master shutoff kill switch to the batterys positive or negative side.
Take the switch connection directly to the post. Nhra rules still mandate a positive side hookup. You run the positive cable to the switch not the negative. It would be easy for something to ground out to the frame i suppose and that would complete the circuit even if the negative terminal to the battery was off. 5 disconnect the positive battery terminal usually red and marked with a sign. Do this first to avoid the possibility of electrical short circuiting or shock neither of which are good for your vehicle or your body.
When you remove a battery from a car you should always disconnect the negative terminal first and then the positive. The other wire from the switch should be properly connected to the original negative wire. The reason for this is because as soon as you disconnect the negative terminal there is no way you can accidentally short the battery when removing the positive terminal.