1: Reversing camera switch. - That is, a switch to lie to the display unit, telling it we are reversing, so the reversing camera displays without the car actually moving backward.

1.1: Disassemble dash to be able to get at the display unit’s wiring. DONE.

1.2: Put a connector inline to the existing wiring. Should hold wires securely, have no visible changes to the car when external things aren’t connected.

1.2.1: Decide upon, and buy connector: DONE. Have gone with a Molex Mini-Fit Jr, 20-pin. This is the same connector as ATX power supplies (without the extra 4-pin connector), so are reasonably easy to find in general-commercial-availablity.

1.2.2: Figure out how to connect the connector, in the car, without major disasembly, or melting bits of the car.

1.2.3: Do so, at least for 12 V (accessory or always-on?) and REV. Other lines can come later.

1.3: Measure current on both those lines. 12 V will be reasonably large, rev should be quite small.

1.4: Make the “new part” for the reversing switch. 20-pin connector male, 12v line goes straight through and to one of the inputs of DPST switch. Other input of the switch is REV line from car. Output is REV line to display. Female ATX connector.

1.5: Insert in, hope it worked!

2: Likewise for the input from the display to the reversing camera. Switch signal line from camera with composite video line from the Pi. Should “ground” lines also be switched, or should they be connected? Do I need to worry about the switch adding interference, or otherwise mucking up the signal?

3: Replace the switches with transistors connected to the pi’s GPIO lines, so it can “break in’ to the display under it’s own control.