Sorry, didn't specify but my situation is the same as OP.....negative terminal is unhooked from the battery completely, and trunk is fully latched.

 

....and if you can't get into the car because you've lost your keys as well!!!!


....last resort, hook up a positive to the junction behind the starboard front wheel, bolted on just behind the strut/spring.

 

I have my keys and access to the engine bay and interior. I can't access the wheel well because my wheel lock is in the trunk. The battery in the trunk is disconnected and the trunk is fully latched.

I need to energize the system from either the OBD2 port or from the engine bay. I tried an OBD2 memory saver cable, got enough power to the system for it to recognize that the door was open, then it lowered the window like it does when you open the door. It then suddenly lost power despite the power source functioning just fine, and I suspect there's a blown fuse now.

I would like to energize the fuse box like I've seen in the picture above, but I need to know how this method was grounded. I'm also open to other suggestions for sure.

 

So have you actually tried the underhood terminals?

 

Yes, tried the jump terminals. Does not power the electronics, likely due to an incomplete circuit.

 

There's a suitable stud protruding not far from that terminal block on my car perfect for a ground as its earth bonded and unpainted.

 

Ok, that worked. I energized fuse F15 in the A-pillar footwell fuse box, which powered the console and allowed me to hit the trunk button. Got everything connected, car started no problem. THEN, I tried to read/clear a DTC with my HP Tuners MPVIv2 and it all went to hell. I can't start the car, I can't turn off headlights, the gauge cluster screen keeps fading in and out......this ODB2 system is very temperamental. Best of all, the trunk is shut again and none of the buttons work to open it. So now I've got a powered dash but unresponsive buttons. I might try F15 again, just to see if that allows me to open the trunk again so I can pull the negative lead to reset the system.

From now on, I'll be going to Jaguar to read/clear DTCs!!