How to Connect a Relay for Car Reverse Camera Installation

When you are installing an aftermarket head unit upgrade with a car reverse camera, the rear view image on the display may be no signal, flickering, or a similar issue. This is most probably the voltage from your car reverse light is not stable, so it can not provide stable 12V voltage to the camera. Because the car rear view camera should be powered with 12V car reverse light. So that the camera can get 12V power from your reverse light.

If your car can not provide stable 12V voltage from reverse light to the camera, then the camera display will be no signal, or flickering. This is a common issue especially for some old cars. If you have a multi-meter, you can also measure the voltage from your car reverse light.

Solution is to connect a relay between the power source and the camera.

At first, you should know what a relay is, how does it look like, here’s a picture for your reference:

relay for reverse camera

How to connect a relay?

  1. Connect pin 30 (blue wire) to battery power source.
  2. Pin 87 (red wire) goes to camera power wire leading to head unit.
  3. Pin 85 (white wire) goes to reversing light power wire.
  4. Pin 86 (Black wire) to ground.

reverse camera and relay wiring diagram

Thanks our customer Gregory Davis who provided the above photo from USA. He solved the camera unstable issue by connected a relay.

part of the relay

Connected and tucked away in side storage panel.

relay connected

Thanks Lance from France who provided these photos and instruction for connecting the relay.

Tips for connecting a car rear view camera

Installing a car back up camera with an aftermarket head unit is not difficult for a professional mechanic. From the head unit side, you should connect 2 cables.

One is the video cable with RCA connector, but please pay attention to the label on the cable, because the RCA cables should come with other plugs which are also with RCA connector, the label may be written as “BACK VIDEO”, or “REVERSE CAMERA VIDEO”, if you have a doubt, do not hesitate to contact the supplier of your unit to confirm which is the video cable for the camera.

The other cable is a loose trigger wire, which triggers the camera to work after you put in reverse gear. It may be labelled with “REVERSE 倒车检测” or “BACK”. If your display can not automatically switch to backup images, you should check this loose trigger wire and see if you connect it correctly.

camera display cables

Got any questions about how to connect a reverse camera or a relay? You can write a comment below or drop us an email to Please provide as much information about your questions or your issue as possible, so we can better help you.