Remove the 450 amp fuse. That's the one going to the starter and alternator.

I was thinking the fuse just plugged in, but I found some pictures showing how it is secured with fasteners. So you could just undo the cable for testing if that is easier to do.

Pics in this thread showing the location relative to the battery:

https://www.jaguarforums.com/forum/s...-issue-230037/

 

​​​​​​Removing cable eliminates both the 250 amp and the 450 amp fuse. Okay on that?

 

Look at these pictures again. Does your arrangement look like that, I mean other than the fire and melted plastic part? You will have to remove the trunk liner for access:

https://www.jaguarforums.com/forum/s...-issue-230037/

Battery power is fed directly to both fuses via the big cable at the bottom. Note how the cable is attached directly to the aft fuse, and a heavy bar brings power to the forward fuse. Don't mess with this common cable, as disconnecting it will disable both fuses.

Looking at the two fuses, the forward one appears to be the one for the starter/alternator. The pic shows 400A, but the wiring diagram shows 450A. Not sure what you'll find, but it should be the heavier of the two fuses. Disconnect this upper cable from the top of the forward fuse (or remove the fuse, but that's more work).

Leave the 250A fuse (aft side) and associated upper cable as is.

If the heavy battery drain stops, then you know it was through the circuit from the 450A fuse. While connecting or disconnecting these fuses, make sure you have the battery ground cable disconnected.

 

Battery charged and installed, (13 volts).
450 amp cable off exit side of fuse.
I will check in about 5 or 6 hours, and again in morning for drainage.

 

With 450 amp cable disconnected, I still had a slight drop in voltage overnight. It went from 13, to slightly over 12.

 

Dead again. Down to 6 volts after 27 hours with 450 amp line disconnected.
Shall I recharge and try it with the 250 amp line disconnected?

 

Okay! You may not realize it, but you're making excellent progress. You've (partially) identified the problem and ruled out one source.

Gotta make a confession here. I had you skip ahead in normal troubleshooting and take the alternator out of the equation. I had been thinking you had a very heavy drain on the battery, and if so, a failed alternator diode was a strong possibility. Most battery drains are much smaller, and won't kill a GOOD battery so quickly. That's why I had you go straight there.

But at this point, I'd suggest to reconnect everything and then start at the very beginning of the normal troubleshooting flow. Here's the link again, open the PDF in the first post:

https://www.jaguarforums.com/forum/s...-drain-123535/


That test has you disconnect the battery ground cable and hook up an ammeter. (If you want to spring for a clamp-on ammeter, maybe $100, you don't have to disconnect anything) After a 60 minute shut-down period, make sure the total amperage is less than 30 milliamps. That's not much, only 3% of one amp. I suspect you will find substantially higher than that. If so, you then get to isolate which circuit is drawing power after the shut-down should have occurred. Lots more details in that PDF. This can be a very slow process, as you repeatedly have to wait for the shut-down period after pulling any fuses or otherwise waking the car, but you will get there. Once again, make sure the battery is fully charged before doing any of this. (Criminy, he sure does harp on that a lot...)

If you do find the current drops below 30 milliamps, and the battery was fully charged at the start of the test, then the battery itself has failed.

 

Okay, not to cut you short, but while waiting to hear back from you, I recharged the battery, reconnected the 450 amp line, and disconnected the 250 amp line. After 24 hours, still at 13 volts. That appears to eliminate the accessories and starter / alternator circuit, I believe. Thoughts, suggestions, advice?

 

I love you!



No worries, this is also a valid method of troubleshooting. Sounds like you are hot on the trail. There are two 250 amp megafuses in the trunk. One is right next to the fuse panel, but you didn't touch that one yet, right? Is the one you disconnected right next to the 450 amp megafuse for the starter? This is the 250A megafuse feeding the front power distribution box under the hood. So if the battery is staying up with this panel isolated, the problem is something fed by that front panel.

In the wiring diagrams, see figure 01.1 for this 250A megafuse, near the top. Figure 01.2 shows the front panel, on the right side of the page. Now the fun really starts, as you have to work through those fuses to see which circuit is drawing power after shut-down.

If you have a digitial meter that can read millivolts, you can quickly determine which fuse is powering the circuit that isn't shutting down. You don't have to pull any fuses, so the process is fairly quick. It's a little hard to explain, but here's a good description (with video) of the process:

https://us.autologic.com/news/testin...e-voltage-drop


Here are the best charts I've seen, print them out for reference:

https://www.powerprobe.com/fuse-voltage-drop-charts/


Alternately, you can pull the individual fuses and wait, but that is a VERY slow process.


Edit: Another easy trick you can do while troubleshooting. Let the car sit overnight. At the panel under the hood, touch each relay and see if any of them feel warm. If so, that means the electromagnet coil inside has kept receiving a signal to energize when it should have been commanded off.

 

Okay, I put the car to sleep with the hood open. Not having a digital multitester, I gave it a shot with my analog. Had no readings across any fuses, but when I went to check either fuse 16, or 17, I got a loud click under the hood. It startled me, and I that's why I'm not sure which one I was on. I had my one lead on the front side of 15 or 16, and had touched on the back side of 16 or 17. (I believe it was 15 and 16, but not sure).
It would not repeat, and I got nothing on any of the remaining fuses. Bought a digital multi tester now, reluctantly. (Being 70 years old, and having gotten by with the same analog multitester for 50 years), and repeated the run the car, put it to sleep, and test for mv across all the fuses in the front panel, to no avail.
Thoughts / suggestions?

 

Not sure about the loud click? Could it have been a relay? Those usually aren't very loud, though. The only loud thing that comes to mind is the clutch on the AC compressor. That can make a loud ringing noise, but I'm not seeing how those fuses are related.

Fuse 15 is for the fog lamps.
F16 is for the horn.
F17 is for the fuel injectors

I wonder if you accidentally blew one of those fuses. Start the engine to confirm the injector circuit is still good. Test the horn and fog lights, too.

For reading millivolts across a fuse, you're going to need that new digital meter. I love my old analog meters (I repair and sell Simpson 260 meters on the side), but I almost never use one around modern electronics. They just draw too much power from the circuit under test and can skew the results. I've got a Fluke 83 (amongst my dozen or so other meters) and it's my workhorse. If you want to take it from me, you will have to pry it from my cold dead hands.

Are you still getting the battery drain? You can always switch back to the method given in the guide, as previously mentioned: disconnect the ground cable and connect the meter in series to directly read milliamps.

 

Got a new digital that measures millivolts. Will test fog lamps and horn fuses tomorrow. Couldn't have blown injector fuse because I ran car today for a bit. Wondering if the click may have unstuck something causing the drain. I guess I'll know in the morning with a battery check. It's still at 12.3 volts.
It didn't sound like a relay in the panel. More like a/c clutch, or something like it. Could have been injectors.

 

All the fuses test good. Whatever clicked while checking the fuses the other day, may have been the culprit. No drainage overnight, or virtually none in the last 36 hours, considering alarm blowing when I open the trunk to test battery, using power locks to open, to access hood, and relock, courtesy lights in car and trunk, etc. Hmm! Wish I knew what clicked, because if it stuck once, it will likely do it again.

 

Any updates? The suspense is killing me.

Even if the battery seems to be holding power now, have you measured the amp draw to confirm the car is properly going into sleep mode?

 

I'm losing a mere .03 volts per day with car parked and a/c turned off, prior to engine shut off, in the event it was the compressor that was stuck, and was the click I heard, during that test.
. Being busy preparing to move soon, I updated a friend that does most of my auto service, and he's coming to take the problem child off my hands today to prepare it for our 650 mile move.
Thanks for your interest, and all the tips that helped to narrow the search. I actually enjoy the challenge, making things right, but timing isn't right for me at this time.

 

I will post results of his diagnosis and repairs.

 

Curious to hear what your friend finds.

I agree the compressor was the likely source of the noise. However, I doubt the compressor itself was the root cause of the fault. The compressor clutch coil (the big electromagnet) is only a consumer of electrical power. Even if the clutch got physically stuck somehow, the electrical command (and battery drain) should have shut off as normal with the engine off.

For the coil to continue drawing power with the engine off, one of these scenarios would have had to happen:

1) The PCM would have had to remained powered and provided the ground to energize the compressor control relay and connect battery power to the coil. Not totally impossible, but also not very likely.

2) The PCM-switched wire that provides the ground for the control relay could have a bare spot rubbing against metal. This would continually energize the relay and connect battery power to the coil. This is worth investigating, but may be hard to find if intermittent.

3) The compressor control relay stuck closed even after the PCM-switched ground signal was removed.

In my over-inflated opinion, a bad relay is the most likely fault and super easy to rule out. At the front power distribution panel, remove relay R8 and pop off the plastic cover. Make sure the contacts are free to open and close. Look for any signs of arcing at the contacts, often seen inside the cover.

If the relay looks good, swap with relay R11 (front fog lamps) for peace of mind. If you rarely use the fog lamps, this relay is basically a nice spare in near-new condition. And if the suspect relay ever sticks closed again, the fog lamps will be on, making it easy to spot. It won't cost anything to swap relays and is simple to do. Cheap and easy, just like me...

 

One more thought: You can easily trick the compressor clutch to engage and release with the engine off. It should make some noise, and then you can compare if this sounded like what you heard. It might be nice to know if you're on the right track as to what suddenly changed.

Engine off. At the front power distribution box, remove relay R8. Briefly connect a test jumper between sockets #3 and #5. Something as simple as a paper clip should work. With the jumper connected, the clutch should engage. Remove the jumper and the clutch should release.

 

That's what he did. He swapped the relay.
Thank you! 👍