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:

a relay for rear view camera

How to connect a relay?

  • Connect pin 30 (blue wire) to battery power source.
  • Pin 87 (red wire) goes to camera power wire leading to head unit.
  • Pin 85 (white wire) goes to reversing light power wire.
  • Pin 86 (Black wire) to ground.
reverse camera with 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
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.

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.

8 thoughts on “How to Connect a Relay for Car Reverse Camera Installation

  1. Hi
    So I have one of your Units and a reverse camera from Cestovet. After installing it in the car I notice that instead one image I got multiple copies of the same picture and its flickering. I took my lab power generator and I gave the camera constant 12Volt. The problem wasn’t solved. So that has to be communication issue inside the unit. I contacted another camera to it and I had still multiple copies o the same picture but not flickering. Weird. Please help
    Sincerely Ray

    1. By searching your email, i can not find your order information with us. If you make sure you ordered the unit with us, you can contact us via email directly for help.

  2. I have the issue that the wiring is correct but the trigger does not work. I can tell it is correct because I attached a bulb to light up when 12v signal is sent to the head unit, however, the unit does not recognize, is there special settings?

  3. Hello, I have a 2005 Ford Thunderbird, and I am trying to hook up a rear view mirror back up camera . It’s an Auto-Vox T2-1 system. Both of the wires going into the reverse bulb are hot. 12v on each. I need help on how to hook this up so that when the car is put in reverse, the mirror comes on. Now it is on all the time. Any help BBC would greatly help appreciated. Thank you

    1. For your reverse light, normally only when you put in reverse gear, it will get power, right? If it’s on all the time, you need to check your wirings.

      1. It’s how FORD wired their backup lights in some models… their backup light is wired with constant 12volt power and use a ground polarity for power… not like most cars in which their backup light is only powered when the car is in reverse.

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