This is a very long answer, and contains much more detail than you probably want. But now that I have an OEM wired tow-mode camera system (and a spare), I likely won't be looking into this any further. So I wanted to document what I've found so far, both for my future self and anyone else who may be interested.
With the 2023 rear view mirror, Ram switched to Magna's ClearView system.
https://www.aftermarketnews.com/magnas-clearview-vision-system-comes-to-market-on-ram-truck/
(I believe for previous years they used a system made by Gentex.)
The Magna ClearView system has a processor module under the driver's seat. Here's a couple of pictures of the PCB inside that module.
View attachment 67194
View attachment 67195
The key thing here is each video input feeds into a
DS90UB954 dual channel deserializer. One deserializer for the left side camera, one for the right side camera, and one deserializer that connects to both the CHMSL camera and also the trailer camera input. Here's a closer look at where the CHMSL and Trailer inputs feed into the DS90UB954 deserializer.
View attachment 67196
There is
no major electrical difference here between the CHMSL input and the Trailer input. There is a slight difference in the filtering for the power injection, but as far was the video signal itself... both video inputs are capacitively coupled directly into two different inputs on the same DS90UB954 deserializer. There is no hardware difference here that would prevent a camera that works on one input from working on the other. So the limitation must be in software.
Before going much further, I probably need to provide a little background information on how these camera systems typically work and what sort of data is actually being passed down that coax. The camera sensor itself will typically have some type of parallel interface. (MIPI is fairly common.) This parallel sensor data is passed to a serializer which combines the parallel sensor data into one serial output. From here it goes through the coax to a deserializer. This breaks the serial data back apart into parallel data that looks very similar to what the camera sensor initially put out.
However, in addition to the video data stream, there are two other very important electrical signals passing down the coax. One of those is electrical power. The power injection on the coax allows the cameras to operate without any additional wiring, beyond the coax itself. The other signal is a back channel control signal. This allows the processor to pass configuration data for the serializer through the deserializer. So power, video data, and configuration control all over one coax cable.
View attachment 67200
For our trucks, it looks like they are using i2c for configuration and control of the deserializer (and ultimately the serializer using the back control channel). So next I started down the path of tapping into the i2c bus that the GW5410 uses to control the deserializer. If anyone else is crazy enough to try this, here is a picture of where the connections are made. (I was working under a microscope to make these connections...)
View attachment 67197
I haven't spent too much time decoding this i2c data. There's quite a bit of it to sort through. I think my next step would be to write a utility to assist with decoding this data stream. However, before I started on that I managed to find somebody (after a year of searching) who sold me a couple of camera systems.
This finally brings me around to looking at what's actually in the tow mode camera system. The part number of the trailer camera is
68506532AA. This is a different part number from the other three cameras used (P.N. 68506525AA). I have not tried plugging the trailer camera in directly (without the repeater) yet.
The repeater itself is very well sealed and the PCB potted. I didn't see any way to open it up without completely destroying it. I did eventually get to the PCB, but the enclosure was completely destroyed in the process.
View attachment 67226View attachment 67227
On the repeater we have another
DS90UB954 deserializer matched to a
DS90UB953 serializer.
View attachment 67228
And since I did completely destroy the enclosure, I designed and 3d print a replacement. (Design here:
https://www.printables.com/model/698394-2023-ram-2500-tow-mode-camera-repeater-enclosure). I did have to replace the fakra connectors as the shrouds for the existing connectors were built into the enclosure.
View attachment 67230