How-to Guide
How to Add a Second Camera for a Trailer or a Front View
Quick answer
Your MK4 gives you two video inputs as standard. Reverse uses the camera input on Harness F and switches over by itself. The second is the auxiliary video input on A18, the yellow RCA on Harness A, and you select it yourself from the source list. Reverse still takes over the moment you shift into reverse.
What this gives you
A view you choose to look at, not one the gearbox chooses for you. Reverse a van onto a site, watch a trailer over a rough track, or see what's in front of a bull bar in a car park. All on the screen that's already in your dash.
Before you start
- A camera with a standard analogue composite output on a yellow RCA. You're feeding a video input, not a second reverse input.
- Harness A, which carries A18. It comes with your unit.
- A video extension lead long enough for the run, if your camera sits at the back of a tray or on a trailer.
- A 12V supply for the camera wherever you mount it.
Step by step
- Confirm which input you're using
A18 is the auxiliary video input, the yellow RCA on Harness A. The reverse camera input is F6 on Harness F, also a yellow RCA. You're dealing with two different plugs on two different harnesses, and they behave differently.
- Run the camera video to A18
Take the camera video lead to the yellow RCA on Harness A. Route it away from power cabling where you can. A video run laid alongside a power run picks up interference.
- Power the camera from a switched supply
Unlike the reverse camera, this one isn't tied to the reverse light circuit. Give it a supply that comes on with the ignition. That way it's live whenever you want to look at it.
- Select it from the source list to view it
The auxiliary video input doesn't switch on by itself. Bring it up from the source list when you want it, the same way you'd pick any other source.
- Test the priority before you rely on it
Chock the wheels and put the handbrake on. Bring up the auxiliary view, then select reverse. You should see the screen switch to the reverse camera and go back afterwards.
- Use a proper break in the run for a trailer camera
If your camera lives on the trailer, it needs a connector at the towbar, not a lead pulled through a door seal. Wire the vehicle side once, then plug the trailer in.
If it does not work
- If you get no picture on the auxiliary input, check the camera is powered. A camera with no supply looks exactly like a wiring fault at the head unit end.
- If you see black or scrambled video, the auxiliary input expects a standard analogue signal. An AHD camera won't display correctly on it.
- If you see the picture roll or go noisy on a long run, that's usually the run picking up interference. Move it off the power loom before you replace the camera.
- If reverse stops working after you add the second camera, check nothing moved on Harness F while you were working on Harness A.
Worth knowing
The reverse trigger switches your screen to the reverse camera input only, and you can't point it at the auxiliary input instead. You only get four camera inputs, front, rear, left and right, where the 360 system was ordered, on its own harness. That isn't fitted as standard.
Still need help?
Tell us your vehicle, the year and what you're seeing on screen, and we can point you to the right step.