12V Switched Ground with light in switch

Thread Starter


Joined May 23, 2020
I recently added a brake controller (Tekonsha P3 Brake Control) to my Toyota Tacoma pickup which has no power switch, and would tend to drain the battery if the truck was not used for several days.
So, I would like to add a switch to open the circuit to it.
It would be easiest to connect to (and switch) the single ground wire to avoid cutting into a bundle of wires to access the hot lead and switch that.
The switch I would like to use is an illuminated three leg switch. One pair of legs (call them 1 and 2) are connected inside the switch, with 1 to 12V+, 2 to the controller, and the third (3) connected to frame ground, toggled open and closed by the switch. The switch indicator light goes on when the circuit is closed. The switch's indicator light is not polarity dependent.
The problem I have is in figuring out how to have the switch light on when there is a closed connection (ie. power on for the controller) without the possibility of the current needed for the light in the switch to flow back to the brake controller.
I was hoping to put a diode (a Schottky 1N5822, 40V 3A) on leg 2 (which is connected to the controller) to prevent current from flowing from the switch back to the controller.
If I have the diode's cathode connected to leg 2, the switch's light turns on when the circuit is closed by the switch. A bulb connected to the same 12V+ source (temp in place of the controller), with center connected to 12V+ and jacket connected to leg 2, turns on when the switch closes the circuit and turns off when the switch opens the circuit.
I would like to verify that no current will flow back to the controller from leg 2; that it will only flow from the controller to the switch. Also, that having that diode in the circuit won't have an adverse effect on the controller.
Any thoughts or suggestions on this?