Hello - I'd like to install a rear dash cam on the glass of the hatch door. Where is the closest spot to find ignition-controlled 12V back there? I know there is a motor to operator the door up and down, but that works without the car being on.
The trailer lighting package in the left rear has the connection you want.
With factory towing package, pin 2 of the trailer IG2 relay (blue wire) is intended to charge a trailer battery, protected by fuse 17 (20A) in the Aux Under-Hood Fuse Relay Box. You may need to place a fuse in that position, and will need to add a fuse in the new wiring to your camera.
The trailer towing controller in the rear is optional, but there are aftermarket pieces you can install. You can duplicate the trailer IG2 relay function without the whole controller, with a little creativity. The trigger for your replacement relay is in pin 12 (yellow) of the connector in the left well for the missing controller. Supply will come from pin 8 in that same connector, a light green wire. Put a small fuse in the holder under the hood, small enough to protect the wiring you are installing. A 2.5A fuse will be plenty to power your new rear camera. DO NOT try and wire the camera to the yellow wire directly; it's passed via MICU and an internal solid-state switch intended only to trigger a relay. This will trigger the relay on when the ignition switch is in position 2 (engine run) only; relay will stay open in position 1 (accessory) and position 3 (start), to support full-current starting, plus it will protect you camera from any possible voltage variations (read: spikes) as the starter motor is engaged then disengaged.
You'll need to route the camera wiring up the rear pillar and across the trim, into the door, and exit where you want to place your camera on the glass. Configuring for regular cable flex without damage between the door trim and the glass will be a challenge. Conventional method is to coil the section so that the twist is distributed over a length of that wire, rather than just letting it flex and fail at a single spot. That "length of wire" needs to be captive so things passed through the window opening or packed high in the rear don't damage the wire. Unfortunately, the blackout detail on the rear glass precludes rigidly mounting the camera to the door trim and letting the glass open independently.
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