If the switch is on the torque convertor can lockup. If the switch is off it cannot lock. In order to get an indicator light what you would do is hook up say an led ground lead to the wire that we are using for the switch and run the positive to a positive power source. Now when the switch is on the light is on and when its off the light is off. Just make sure that you splice into the ground on the side that will be disconnected otherwise the light will always be on.