Hi all, long time lurker/first time poster here with a question I couldn't find any other posts on.

I have a 2002 XJR (with the R1 package, most likely not relevant here). Owned it for 5 years, zero issues aside from regular wear items. Great car.

I've had the car stored in my garage for the past 2-3 months due to winter, put it away kind of late due to warmer than average weather in my area. Pulled it out yesterday to find the battery dead ... hindsight is always 20/20 and I should have used a tender, but the battery was fairly old anyway.

Not my first rodeo in jumping the car so I began the usual procedure... unlock driver's door, pop the hood, locate the underhood terminal next to the passenger side shock tower to pop the trunk and access the battery for jumping or removal. I have one of those 1000amp portable battery jumpers that I keep charged at all times for these situations. Here's what occurred:

- I attached the portable battery, red clamp to underhood terminal, black clamp to body/ground as I have done at least once before
- I turn the portable battery on
- The car's security system immediately starts counting down due to myself accidentally leaving the driver's door ajar
- I reach into my pants pocket, only to realize my key fob is not inside
- The car alarm starts blaring
- I frantically begin searching for my car keys, hoping to locate them before my neighbors murder me (it's just a little past 8:00am on a Sunday)
- I locate my keys in my jacket on the garage coat rack and jump into the driver's seat, forgetting that I have left the jump pack connected to the underhood terminal
- In my panic I put the key in the ignition to silence the alarm, but panic and turn it to the ignition setting
- The car cranks for half a turn and goes completely dead
- Before dying the sunroof inexplicably opens itself to the vent position
- Further attempts to pop the trunk using the underhood terminal are useless. There are no lights on the dash and no sounds from the car. I can not extricate the battery from the trunk or check the trunk fuse box at this point

Basically in my panic I did a Really Dumb Thing and am expecting that this will be a Very Costly Mistake, which I am fully prepared for.

I am just hoping that this forum might have pointers for where to start my troubleshooting. My assumption based on the behavior of the car is that I shorted the underhood circuit which allows the trunk to be popped, but I'm lost on what this circuit might connect to and the potential damage. I'm on my lunch break currently, but after work I plan to go through every fuse that I have access to and check/replace any I might have blown.

Looking for any advise on where/what else to check first. Criticism of my dumbass also welcome. Depending on how this goes this may evolve into a part-out thread, though hopefully not.

Thanks for reading.

 

How about opening the trunk with the key and installing a new battery?

 

Key unfortunately does not open the trunk

 

Tried some WD40, and also pressing down on the trunk lid when turning the key?

 

Is it a green key?

use the jumper again and use the trunk button on the left side of the steering column.

 

As advised, you should be able to open the trunk with the key (unless you only have the valet key). If the key does not work, try connecting a 12V power supply, not from your jump starter but using another external battery (can be a smaller one but should be fully charged) to the same bulkhead terminal. The jump starter you used is not really designed to crank the engine on its own but together with the battery which still has some charge (not completely dead). These jump starters are actually 10.8 Volt and are not suitable for general 12V power supply. They have lithium batteries inside and a protection circuit which has probably cut them off due to overload caused by attempted engine crank with totally dead car's battery (the jump starter should be fine if you recharge it).

Before connecting the supply, close and lock all doors and disconnect the "hood open" switch located near the hood hinge at the RHS. With this, the alarm should not go off but have the key fob ready anyway and, if the alarm still sounds, just press the "unlock" button. This time, do not attempt to crank the engine.

If the external battery still does not power-up the systems, try with connecting it to one of the terminals at the engine compartment fuse boxes, i.e. one of the terminals via which a short thick wire connects the small and large fuse boxes.