Connect another battery between ground and the positive post in the engine compartment. Some jump starters have electronic control which will activate the power from it only if there is battery (even weak) connected to the car's wiring.

 

I tried two types of jump starters on the underhood posts. One standard and one Li ion. But both gave polarity errors and wouldn't flow any current and I didn't have another battery available.
I was following the instructions found in another thread on resetting your TPS, so I had removed both battery cables, hung them together and gone around to click the ignition on and off to clear residual current in the system when the trunk blew closed without separating the connected cables. Consequently, no circuit to be made with no power source and both cables hooked together.

So, I went to the sngbarratt.com site to find the appropriate trunk parts diagrams and grabbed a flashlight. The license plate holes, actually slots are pretty narrow so I drilled a 1/2in. hole midway between the lower slots to get a better view inside. I knew where the latch mechanism should be, but not what part of it moves. I could find the rods from the release button and the key lock, But I couldn't get either to move the latch. Too much flexion and lateral play in the rods.

By shining the flashlight at various angles and through different slots and holes I narrowed down the location of the latch mechanism and, using a hooked coat hanger through the lower right plate hole, was able to hook the mechanism, pulling it to the right to trip the latch. Voila! I'm in!

Many thanks to all the contributors in various threads in the forum who provided ideas and direction for me try through their posts!

 

To replace fuel pump, i disconnected the batery. shut trunk. The key wont open the trunk ....mechanism appears to work , latch is tight. pushing down on trunk doesn;t work IDEAS?

 

A lifesaver:
2000 Jag XJ8 127,000 miles.
I diagnosed each component in the system.
Then I saw this about the wires at the trunk RH hinge.
I inspected and found them broken and had been fixed previously.
So I added 3" to both broken wires. Red and Black
This forum input was wonderful. that would be terrible to run down without knowledge of the history of the recurring problem

Thanks.
Gary in Manchester TN.