I opened up the case to expose the bare LCD and driver board. The case is just two pieces of plastic snapped together, so I pried it open with a screwdriver. You can see the original input wires connected to the board: red – 12-24 VDC, black – ground, yellow – composite video 1, and white – composite video 2.
I removed the original wires and connected the three wires shown below: yellow – composite video, black – ground, and blue – 5 VDC. The blue wire is (thin) 30 AWG wire that is easily soldered onto the PCB.
I connected the three wires to the Raspberry Pi as shown below using a TRRS connector: yellow – composite video (S), black – ground (R adjacent to S), and blue – 5 VDC (pin 2 of the Raspberry Pi connector).
Here are the relevant /boot/config.txt settings I am using.