I've got the BEMM; there are so many references to ignition feeds and ignition switches and relays and so on.
This is clearly the most relevant bit:
If a positive (+12V) engine run signal is required, it can be done by using the switched ground to control an ignition fed relay, to give this output.
Ignition
Pin 4 - Ignition signal is protected by a 10A fuse. It is +12V active at ignition positions: Accessory (1) and Run (2). It is not active at Ignition OFF (0) or Crank (3). Whilst it can drive equipment
directly it is recommended to use this feed to control a converter fitted relay, especially for high current applications.
The pin 4 it mentions is under the driver's seat on the vehicle interface connector.
Honestly this manual scares me a bit! So much complexity designed in.
What is the switched ground mentioned above? Can I just take a feed off this pin 4? Is there an easier way to do it without taking the seat off? I'm a bit bewildered. Still haven't found a reverse feed to wire my camera up to in the front of the vehicle yet either!