Can be done but it may be a rather technical process.
A rather nerdy mate of mine managed to do it with his BT50 but he ran into a maze of technical issues including 'non-compatibilities' between the two systems. But he's the sort of guy who makes up his own power supplies/DC to DC chargers and the like, just because he likes to, rather than buy a commercial product.
Not knowing the actual screen in the Hilux I wouldn't be certain but it should have a video in plug on the rear of the unit. If that is the case a feed from the camera on the rear of the caravan should be possible.
I have done it with my Landrover. It was rather difficult and was not just running a video wire to the back of the unit. The car has 2 cameras, front and rear, so I had to add switches to view the caravan camera, the front or rear or all at once. This is all controlled from the dash screen. It is not something I could have taken on, as I have little understanding of electronics. But the AULRO web site had detailed instructions and parts required. Your main issue will be to "isolate" the car camera when the van is connected, or have a split screen on the dash unit.
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16.5 Discovery 4 with a few mods and New Age MR 16' Deluxe
I have a reverse camera but others who have tried to add one into their system, it's generally a challenging task. I would not recommend the pain unless you are up to the task. Look at forums on your particular car & hopefully someone has done it. Good luck!
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My plan for my Navara D40 is to have the caravan camera powered by the sidelights which gives me easy control over selecting the camera when driving or when reversing. I intend replacing my head unit with An Android one which supports multiple video inputs. Doesn't help your display requirement but the powering by sidelights seems a logical step as it allows you to get a rearview while driving.
Mikel,
With my set up I can see all three cameras individually (front, rear and caravan) while driving or all three on a split screen. When the van is not attached, the car can display front or rear or split screen, both. I forget the special piece of electronic equipment that did this switching for three cameras but I know it came from Germany and was about $35 for this tiny black box with lugs on it. The advice I followed was after a lot of people tried to do what you propose but had varying outcomes once the van was not connected as the head unit was still trying to find a camera that was not there. I agree with you that until I bit the bullet, it was a pain having another screen mounted on the dash for the van camera, and I was never happy with it. Now its just as if the extra camera was part of the car and not an add on. Plug in the van and the cars suspension and handling characteristics automatically adjust (no WDH on a LR) and plug in the camera and the screen automatically adjusts for the extra camera. I would look at the Navara web sites and ask the questions. Most on these forums will help you out and often have a solution as I found. Good luck!
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16.5 Discovery 4 with a few mods and New Age MR 16' Deluxe