Have good battery, good ground to body, power in fuse panel next to it, but car is totally dead. No lights, no crank, no remote function. Nothing!

 

I hope to have a little free time tomorrow to dig through the wiring diagrams. With any luck, I can find some basic circuit that should work regardless of key position, etc. That would be a good place to begin troubleshooting.

In the meantime, a little recent history of the car, please. A daily driver suddenly acting up out of the blue? Been stored all winter in the garage? A derelict freshly dragged out of a field? Any recent work?

While waiting, please connect a battery charger overnight. I highly suggest an automatic charger with at least a ten amp output. A trickle charger won't cut it.

 

Not driven much, but put new battery in Feb. 8th, 2 days later dead. Replaced as assumed defective, and been fine. Parked car outside garage last week, to paint in garage, and today, nothing, when wife needed to use it. Put charger on it, didn't appear to need charge. Did 10 amp charge 2 hours, hooked up cables, and nothing, no trunk light, no remote operation, nothing. Got power at battery, and fuse panel next to it.

 

Bear in mind 2 hrs 10A is hardly anything and if the battery has been flat a while it just may not accept charge whatever you do.

 

Okay, weeding through the clues here. Not trying to bust your butt, just trying to figure it out and may be asking more questions.

1) Please define "got power at battery". Are you taking a voltage reading with a meter? If so, what voltage did you record? Please be aware that UNLOADED battery voltage doesn't always mean much. If low, yes, that is a problem. But if the voltage at rest seems okay, the voltage may drop precipitously under load when it really matters. I have run into this many, many times in my line of work. If you are seeing something like 12.0 or 12.2, that is almost fully discharged. I'm not a big proponent of determining battery state of charge by testing voltage, as it is so easy to get inaccurate results.

2) From your previous battery going dead, it's possible you've got some undiagnosed battery drain as part of the problem.

3) Getting back on my soapbox to make sure your battery is fully charged before beginning any diagnostics. Two hours at ten amps won't make much of a difference if the battery is fully discharged. Is your charger automatic? If so, you should be safe to leave it running overnight. I would highly suggest taking the battery to have it tested for state of charge and overall health. Do not assume (Danger! Danger!) your battery is good because it is new. Also, most new batteries are not fully charged at time of sale, so expect you will need to charge it.

4) So even though I've said unloaded battery voltage doesn't always mean much, make sure you are seeing at least 12.6v before continuing.

5) Read step #4 again.

6) Read steps #4 and #5 again.

7) Read steps #4, #5, and #6 again.

8) It took a little digging, but I found 2 circuits that operate via battery power and don't require any modules to be energized. These will be good to use for preliminary troubleshooting. Wiring diagrams here:

http://www.jagrepair.com/images/Auto...cal-2005on.pdf


See figure 11.4 or 11.5 for the passenger seat. With your battery fully charged (note I keep harping on that...), see if the seat responds to any of the control buttons. If not, check fuses F11, F19, and F37 in the trunk and try again.

See figure 19.1 for the cigarette lighter. Turn the key to the ACC position. See if you have power at the lighter socket. If not, check fuses F2 and F56 in the trunk. Check fuse F26 in the primary junction box (inside the cabin, near the right front door hinges). If still no joy, locate relay R10 in the trunk. Place your finger on it and have a helper cycle the key from Off to ACC and back. You should feel the relay click.

9) One last quick test. Hook up your voltmeter to record battery voltage. Remember, you should see at least 12.6v. Turn the key to Run (not Start yet). This should power up most modules and put a partial load on the battery. Record the battery voltage again.

 

I'd been dealing with the same "electrical/battery" issues for 4 years or so with my 2000 Stype Jag. Had it evaluated and worked on by many mechanics, even ones at the Jag dealer. I went through about 4 batteries in 3 years. Every time my car was being repaired or evaluated they would check the alternator, even had it on diagnostic machines for 3 weeks once, and the alternator would show on the meters as good. A few months ago, and after a cold spell, the car just died - no life whatsoever. The battery was 3 months old and wouldn't hold a charge. My son, a mechanic friend and every other amateur mechanic said it was probably the alternator, at which point I would argue with them due to past exams. But I was at my wits end and told the mechanic to just put in a new alternator. That plus a new battery and my car runs like it hasn't in a long time. The mechanic said the alternator was the original - 20+ years old - as it had the Jag logo on it. I believe him as I'm the 3red owner of this car and I have all papers of work done on the car.

 

Removed battery from car, giving it a bench charge. My multi tester read only 6 volts.

 

That's dead, dead, dead. The charger may have trouble bringing the battery back to life.

Most likely you have something drawing down the battery while sitting overnight.

 

Reading 12 volts now, but not close to full charge according to guage on charger.

 

Sounds Like Battery was either faulty or is now faulty due to excessive discharge. Chargers respond to battery resistance and can indicate full charge when not. What is the draw from the battery when first connected? Does it spark on contact with terminal?
My S still going fine but lost the back wheel mudflats in flood waters today..

 

It took 12 hours, but got full charge. Measures about 14.3 volts on analog multi tester. Will install, and check voltage daily to determine if there's a draw when sitting.

 

Glad to hear the battery wasn't completely toast. 14.3 at rest is actually high and indicates a misleading surface charge. Turn on the headlights for about ten seconds to dissipate the surface charge. Measure again, and this will be a more accurate baseline.

 

Okay, will do.

 

Good advice, but I'd like to add one caveat to the "spark test". On pretty much any modern vehicle, you will get a tiny spark when reconnecting the battery. Any kind of load present will cause this. Heck, even just having the trunk open is enough, as the circuit for the trunk light is ready to go, just waiting for power. And of course you've got all sorts of computer modules that will power up immediately. I think the trick is how big is the spark? It's difficult to rate the intensity of the spark and say what is good and what is too much. If big enough to startle you, that's definitely too much though.

The only situation where you won't get a spark is with a total stone-age vehicle. For example, my 1948 Jeep has 0.000 amp draw when parked. No electronics on it whatsoever, so no spark. My 1984 pickup is nearly as primitive, but it has a modern stereo with a memory circuit, and it draws a few milliamps at all times. I'll get the teensiest spark from that, or more if I have the door open and the dome light is on.

From the Unsolicited Advice Department, since we are talking sparks: Years ago, I was taught to always blow on a battery for a few seconds before reconnecting the ground cable. This is especially important if you've just recharged the battery. The charging process creates hydrogen gas which can accumulate. Think Hindenburg. Blow on the battery to dissipate any potential explosive atmosphere before introducing a spark.

For tracking down any potential drains on the battery, here's an excellent primer. It explains how the car needs about 60 minutes before all computers go into sleep mode:

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


If you get a large consistent amp draw, more than just some module staying awake, you could have a failed diode pack in your alternator.

 

the spark was normal, when I hooked up the negative terminal. Started and ran for about 2 minutes to set clock. Next day voltage check read 12 on multi tester. Will check daily, undriven for a couple days to determine if alternator issue.
My A.D.D. had me bouncing around to several other indoor projects yesterday. It's pine pollen season here in SC. Facemasks are multi purpose these days, in and outside.​​​​

 

What is the resolution on your meter? I'm not a big fan of determining a battery's state of charge based solely on voltage, but it can be done as long as you are aware of the limitations. One big gotcha is there is only a fraction of a volt between good and bad. Look up a chart online and generally 12.6+ is fully charged for a lead-acid battery. 12.0 is maybe 10 or 20% at best, essentially discharged. Your meter needs to be able to discern such a minor difference. And if using such a chart, make sure it is for the correct battery, as lead-acid, gel, and AGM are all different.

So if you're really seeing 12.0, and the battery had been fully charged the day before, either the battery itself has failed and/or there's a big drain present. You can differentiate this by fully charging the battery and bleeding off the surface charge. Disconnect everything, measure the voltage, and compare 24 hours later (or longer). A good battery will barely drop. A bad one will self-dacay.

Check your alternator output, too. With the battery fully charged (note I keep stressing that for troubleshooting), connect your meter leads directly on the battery posts. Start the engine. On a 2003+ model, you should see approximately 14.5 for a few minutes, gradually tapering off to about 13.5.

 

Didn't get to measure voltage yesterday, due to severe storms throughout the day. Checked this morning, and battery flat lined again. Doing another bench charge.
From 12.0 to 0 in less than 48 hours.

 

All right, making some progress. Sounds like your battery has morphed into an oversized paperweight, or some major external drain is present.

If such a heavy drain is present, a failed diode pack in the alternator is the most likely culprit. With the battery disconnected, pull the starter megafuse in the trunk. This will isolate the starter and alternator, as they share the same heavy cable from the trunk to engine. Reconnect the battery with this fuse removed, and see if the battery voltage now stays where it should be.

 

Can I just disconnect the cable that goes to the megafuses?

 

If not, which megafuse do I remove, the 250 amp or the 450 amp?