Disclaimer. This is what worked for me, but copy anything like this at your own risk!
The van is a 2018 Plate Ford Transit Custom 290 Limited, L2H1.
It took a little bit of probing with the multimeter to find suitable places to install a fuse tap on this van. Our dashcam (Auto-Vox V5 Pro*) required a permanent and switched 12v connection, so these are the ones we used. Also note that I’ve rotated the diagram round to show it as it appears in the van. For the ground connection there was a suitable nut near the ODB port to the right of the fuse box.
Other things to note are the use of tiny little “Micro 2” fuses.
I was advised to avoid tapping into fuses that power critical safety features (ABS etc), so make sure to check your own booklet that these locations are also safe for your van. This van doesn’t have any rear windows, so that’s why we chose these particular fuses.
It’s worth also noting that this van has a huge lump of black plastic where a rear view mirror would usually be. Fortunately there was a mirror mount under there, but unfortunately the front camera is largely blocked by the plastic. We’re currently prototyping some solutions for this.