How to add a second camera for a trailer or a front view
A standard MK4 has two video inputs. Reverse uses the camera input on Harness F and switches automatically. The second one 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 rather than one the gearbox chooses for you. Reversing a van onto a site, watching a trailer over a rough track, or seeing what is in front of a bull bar in a car park, all on the same screen already in the dash.
Before you start
- A camera with a standard analog composite output on a yellow RCA. The auxiliary input is a video input, not a second reverse input.
- Harness A, which carries A18. It is supplied with the unit.
- A video extension lead long enough for the run, if the camera is at the back of a tray or on a trailer.
- A 12V supply for the camera at wherever you mount it.
Step by step
- Confirm which input you are using
A18 is the auxiliary video input and it is the yellow RCA on Harness A. The reverse camera input is F6 on Harness F, also a yellow RCA. They are 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, because a video run laid alongside a power run picks up interference.
- Power the camera from a switched supply
Unlike the reverse camera, this one is not tied to the reverse light circuit. Give it a supply that comes on with the ignition, so it is live whenever you might want to look at it.
- Select it from the source list to view it
The auxiliary video input does not switch on by itself. Bring it up from the source list when you want it, the same way you would pick any other source.
- Test the priority before you rely on it
With the wheels chocked and the handbrake on, bring up the auxiliary view, then select reverse. The screen should switch to the reverse camera and go back afterwards.
- For a trailer camera, use a proper break in the run
A camera that lives on the trailer needs a connector at the towbar rather than a lead pulled through a door seal. Wire the vehicle side once and plug the trailer in.
If it does not work
- 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.
- Picture is black or scrambled: the auxiliary input expects a standard analog signal. An AHD camera will not display correctly on it.
- Rolling or noisy picture on a long run: that is usually the run picking up interference. Move it off the power loom before you replace the camera.
- Reverse stops working after adding the second camera: check nothing was moved on Harness F while you were working on Harness A.
Worth knowing
The reverse trigger switches the screen to the reverse camera input only, and it cannot be pointed at the auxiliary input instead. Four camera inputs, front, rear, left and right, exist only where the 360 system was ordered, on its own harness, and that is not fitted as standard.
Related guides
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