The safety key that comes with the CM/SPCM1936 installs in the safety key/charging port near the top of the handle. The key works by making/breaking the power connection between the top and bottom connectors. The third connector in the middle is for charging.

If the safety key is lost, it is possible to make a shorting lead from some 30A Anderson PowerPole connectors and a short piece of 12-14AWG wire if you have the right crimp tools or soldering skills. However, you are much better off getting another key as this fix DOES NOT STOP YOU FROM ACCIDENTALLY CONNECTING THE WRONG TWO CONNECTORS AND SHORTING THE BATTERY. I'm not sure what happens next if the wrong connection is made - maybe a breaker trips or maybe some wires melt - not good things! But this can get you going in a pinch if you are stuck and only costs a couple of bucks to implement.