I recently traveled away from home for 3 weeks.
On my return, the new battery installed in my XJ6 Ser 3 was totally depleted.
Lights etc, were definitely turned off...
A short, but where to start?

 

How old is the battery?

You can try this to start....

Disconnect the + battery cable. Put a volt meter between the positive battery terminal and the disconnected cable. Usie a DVM on the 20V scale, a 5$ Harbor freight one will suffice if you don't have one. The DVM will register the potential difference of the draw. Note that number. Remove the fuses one at a time and note if the number on the DVM drops. When it does on one or more curcuits, that is the circuit with the draw. Once you've identified the circuit you can figure it out. Things like aftermaket alarms, faulty alternator diodes, aftermaket radios and other accessories which are sometimes wired incorrectly are typical culprits.

Sometimes older cars with older computers and questionable grounds just do this and is the reason battery disconnects were popular in the 70's and 80's....you can use one of these latching relays to conveniently disconnect the batter from inside the car.
Intellitec RV Battery Disconnect Relay Solenoid RV camper motorhome 01 00055 000 | eBay

Be sure to wire the starter to the battery side. Since your jag is a convert you may also want to put the constant for the ECM on the battery side of the disconnect also if your LT1 is computerized with an O2 sensor so it doesn't loose it's learned values.

 

As above.

Also take note of any "aftermarket" items, such as alarms, imobilisers, etc. These are very common battery drain sources.

When doing exactly what has been suggested, I always disconnect these items first, and then start with a stock standard car. Proven so much easier over many years of this nonsense.

 

If you know how to use a multi-meter, set it to amps mode (current, milli-amps), disconnect the negative battery post and set your multi-meter between the negative battery post and the battery cable you disconnected. Close all doors and let the car settle for 5 minutes. The drain should be in the single digits (a few milliamps) if any at all. If the drain is significantly more, then start removing the fuses one by one until you find the one that causes the reading to go down to normal.


You have then found the circuit where the drain is happening and you can proceed from there. I used this technique a few times and it *always* works.

 

My Multimeters are HF sourced. One analog and the other digital. They are on a shelf in their original boxes. and, with the instructions on their use.


I've another that I've not fooled with much. it reads by induction???


But, test lamps are still in my box. Bright glow when in probe so dim, or none still tell a tale.


Got fooled by the lamp a few months ago. tracking a circuit for my absent brake lights. Dim, why, bad ground, bad connectors? Nope, dying battery!!!!!


Carl

 

Low Tech Check:

1) call someone you really trust, and give the car keys to that person,

2) get inside the trunk and have that person close the lid,

3) check that the trunk light goes off when the lid is closed.

4) after confirming that it does or doesn't, tell that person to open the trunk lid. (that is why you need to trust that person, and that's why you give him/her the car keys in case the electric lock happens to lock the trunk lock).

Test over. Next test:

5) check that the glovebox light goes off when you close the glovebox door by first checking the push-switch, even though the glovebox light does not come On without the Headlight switch being in any of the ON positions.

6) check the car at night in the dark to see if you see any light ON, particularly the little lights mounted on the rear of all 4 doors below the door catches.

 

If you're alone or cannot find anyone that you trust to let you out of the trunk, use your smart phone for video recording, start it, prop it in the trunk towards where the lights are and close the trunk. Open the trunk and review the video. Easy.

 

When mine had this problem, i chased it forever, as it was intermittent turned out to be the trip computer!, hopefully your issue is one that is always there!!! Some times i could leave the car a week and not have a problem, some times it would be dead after sitting overnight!!!!

Good Luck!

 

I dunno if I'd go for the locked in the boot thing.


But, an old type house hold door bell, some wire an old bulb and some soldering.


Boot open, bell rings. Boot closed, should be quiet, if not, inspect for the activating lever and adjust til it does.


leaned something!!! My Jaguar doors will unlock with battery disconnected, but will not lock!!!


Gotta get around to changing the starter. Almost warm enough yesterday. But, used time and energy on an errand and reassembling my Briggs and Stratton project. No luck, no fire yet. it will have to wait, spring time mebbe.


Carl

 

weattg44's cell phone video camera is the best suggestion so far to check the trunk light goes off when you close the trunk lid.

but if you don't have a cell phone camera, and you don't want to get in the trunk, then by all means build Carl's alarm system.

another option is to remove one of the Tail lamps and one of the interior upholstery side panels, and look through the openings to see if there is any light inside the trunk.