My "kill Switch" literally looks just like a light switch from your house. It is in a square metal switch box that is mounted on the right side of the opening.
It breaks the 12 volt
negative DC connection from the Univolt to the battery.
Mine is very obvious. It is the only switch in the rear compartment.
I have actually installed a second switch that disconnects the 120 volts feed to the Univolt.
I installed the new switch within the box that has the Polarity indicator in it. The polarity indicator lets you know if you have the 120 volt shore power connected bacwards. It is a small round red light.