Here's the Mk2 (empegCar) +12V PSU section.

1. The outside (negative) contact of the DC power jack.
2. A ground screw, useful for probing.
3. The NEG(-) contact for the black wire (unplugged) from the docking connector.
4. A small coil that connects the fuse to the empeg ground plane -- the contact is deep inside the hole here.
5. The other contact of the small coil (I don't know which contact is which).

What you should do, is measure ohms between all combinations of those red dots, plus across the two contacts of the fuse itself, and post your complete findings here.

The ground circuit actually goes from points 1 and 3, through the through the coil (points 4,5), after which it finally connects to ground/chassis (eg. point 2) of the rest of the empeg.