Finding the positive terminal of the rear backup light

Thread Starter


Joined May 22, 2020
I am not familiar with the modern car circuit design and was hoping some advice on finding the positive/ground wires. I could not find the wiring diagram for my car online.

I have a 2015 Mazda 5 and I am installing a rear view camera which requires power from the backup light. Each light bulb has two wires, positive and ground. Shod I do continuity test with a resistance meter by using one of the wires goes to the bulb and another test probe on a good ground from the chassis? or should I measure the 12v by putting the car in reverse with the same connection and see if there is voltage ( yes: positive; no: ground)?

I ask because the continuity test seems simpler and does not require power. But I noticed some modern cars has light control module or relay so maybe the ground wire is not grounded when not energized?


Joined Mar 19, 2019
Yes and for Automotive you use a continuity tester like this:
You connect the aligator clip to the nearest bare metal (ground) and test with the probe. When the light in the handle comes on you have found power. So the circuit must be hot/on.