Rand McNally Backup Camera (how to defeat the 2.5mm jack)

I recently purchased a Rand McNally TND720 unit. One of the main reasons I went with this unit was it has built-in Backup Camera support. I use 2 backup cameras and wanted to eliminate the extra 2 monitors in my truck cab. I figured the TND720 and a video A/B switch would suit my needs just fine.

Surprise !!!! Rand McNally partnered with DieselBoss to develop a VERY non-standard video interface; they use a 2.5mm TRRS connector. To make this issue worse, the backup camera offered through DieselBoss costs $150. I decided to modify my existing cameras ($29.95 at Fry's) to fit the TND720. I quickly learned that finding a 3-ring, 2.5mm male plus was tough. Even tougher was trying to figure out how they actually wired their interface (e.g. which segment of the connector is ground and which is video).

I finally gave up on making my camera interface fit the TND720 and decided to make the TND720 fit standard, RCA-type connectors for cameras. I cut a small hole in the back of the TND720 case, directly below the video-in connection socket, just large enough to pass a common video cable through (one end of the cable was stripped, the other end has an RCA connector on it). I carefully removed the screws from the case of my TND720 and took the unit apart (be VERY careful not to disconnect the screen interface cables from the circuit board !!!). Once the unit was layed open, I inserted the video cable through the hole I cut (wrap the cable with several rounds of electrical tape immediately on the inside of the case to keep the cable from being pulled back out) and simply soldered the 2 wires from my own video cable into the existing solder joints on each side of the 2.5mm socket. The ground wire goes on the outside edge of the 2.5mm socket; the video wire goes on the inside edge (between the 2.5mm video socket and the 3.5mm headphone jack). I layed small pieces of electrical tape on top of the circuit board to prevent any stray ends of the video cable from shorting out, then reassembled the unit.

I connect my 2 cameras to a video A/B switch, then plug the A/B switch into the new RCA connector that sticks out the back of the TND720. My video image is crisp and clear, and I accomplished my entire project for under half the price of a single, DieselBoss camera.

There are some drawbacks to my course of action that I should make clear:
1) the warranty is nullified by what I did (understandably), and
2) there is no support for this modification from Rand McNally (of course, they offered no support for where the find the correct 2.5mm jack and/or what the wiring diagram was supposed to be !!!)

If you're not comfortable taking electronic gear apart and/or soldering small connections, this is not a project I'd recommend. Nearly every town has an electronic shop and/or a geek, though