...and I found my document where I cut and pasted the instructions that I found right on this forum. May only work on a gen 1 Ridgeline, but here it is for your reading pleasure.
It can be done! Aftermarket rearview
camera using the factory navigation plug. No need for a video converter or to find the backup light wire under the dash! Total cost was about $70.00 and about three hours of work. Best of all you don't need to spend $300.00 on a video interface!
The reverse signal is already in the navigation unit so when you put it in reverse it automatically switches the video display to the rearview
camera. Thanks to PUG and his wiring diagram I was able to figure out which wires to use. It did take a little courage and some trial and error to get it working. See PUG’s diagram here
Backup Camera Question
The back of the navigation unit has a seven (7) pin plug for connecting the factory backup
camera. Pin one (1) on the navigation unit is the pin all the way to the left. The Molex plug that I used is a six (6)-pin plug.
Plug type to use is a Molex, part number is WMLX-103. Available from
www.Frys.com for $2.85. Frys part number is 1899306.
The factory plug on the back of the navigation unit has a pin configuration as follows:
Pin (1) is a constant 8 volts dc. I assume that is the voltage the factory
camera uses but its not enough to power an aftermarket 12vdc
camera.
Pin (2) is the video ground or shield
Pins (3 & 4) are not used
Pin (5) is the video line (center pin)
Pins (6 & 7) are jumpered together. I’m not sure what they do but they have to be jumpered together.
Although there are seven pins on the factory navigation plug you only need four of them to make it work. Looking at the picture below Pin (7) would be all the way to the right. As you can see it is jumpered to pin (6). This plug needs to be inserted into the back of the factory navigation unit under the drivers seat so that pin (1) on the left is not used.
In the next picture below, the plug is inserted so that the pins all the way on the right are used and pin (1) has nothing on it.
According to the factory manual, pin 6 is
Camera Shield ("shield for terminal No. 1 to No. 7") and pin 7 is
Camera Adaptive ("Control signal for rearview
camera"). A bit cryptic, but I suspect that pin 7 is the sense line that tells the Nav unit that a
camera is present (it knows somehow). So what you did was ground that signal using the shield ground, enabling the function.