To relay or diode, that is the question. Well, firstly you need to know what role each component will play in a circuit.

A diode is meant to conduct power in one direction and has the ability to allow currents to flow through or not – depending on the direction.

Relays are switches that open and close contact points to other circuits – basically controlling a circuit by a low power signal or to control multiple circuits with one signal.

So, if you’re looking to add lights to a trailer or boat and be able to manually control them or have them come on automatically when you’re in reverse, this diagram uses a relay:

Oznium offers a relay that’d work:

Extra Information


Here is my project:
I am wiring a set of courtesy lights to a boat trailer. I want these lights to come on when the truck is in reverse and also be able to activate them with a manual switch in the cab.
My concern with this setup is that most automatic transmissions are shifted electrically now, and I don’t want to back feed the circuit and shift the tranny into reverse when I am not behind the wheel.

My questions is would it be easier / better to use relays wiring this circuit or diodes? Can anyone suggest a wiring diagram for this circuit?

Thanks in advance!

Phil Oznium Owner

A diode would likely work (you’d have to make sure you get a large enough one to handle the current).
Or here’s a nice diagram for you which shows how to do it with a relay.

I’m assuming the stock reverse light circuit it positive switched (with a constantly connected ground wire).

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