Since the regulator is inside the alternator, someone is blowing smole somewhere! But the grounds and the bulkhead fittings are certainly worth checking. And BTW, the charging circuit on these caqrs is straightforward and ANY automotive electrician with even average skill SHOULD be able to diagnose this fairly quickly.

You have checked the alternator belt tension and made sure the belt is not somehow contaminated with oil, right? You need to determine if the problem is the battery, the alternator or the wiring. Go back and read Brutal's post about the voltage drop from the battery to the alternator. I would add that you should also check the voltage drop from the alternator case to the battery negative terminal for the same voltage.

 

I think I misquoted the guy. He's pretty sharp. I believe he was talking about the ignition link to the alternator and I was getting confused. He was talking at a ninth grade level, and I'm at recess in the third grade.

Well now, that would take all the fun out of chasing the rabbit down the hole, now wouldn't it! : )

I'll be doing a load test on the battery tonight to definitively take that out of the equation. The belt was in beautiful shape, no oil, and appeared to be under good tension. Once we have everything reassembled and can start her up, I'll double check for slippage.

I have a list as long as my arm of voltage/resistance checks to perform tonight, so hopefully I'll have identified my variable before midnight! Once again, I appreciate everyone's help. . .

 

Can you determine which relay is flipping after 5 minutes of running that seems to cause the problem ? It seems like a relay closes and current goes to ground. Like whatever that relay is powering is shorted out. Just a wild guess.

 

Jim, I tried to identify which relay it was, but I couldn't put my finger on it. It seems to be one of the relays located under the tool tray/bulkhead area. There are a bunch there, so I couldn't pin it down. I switched them all up, so I'm pretty sure it's not a bad relay. I agree that it could still be what the relay is turning on that causes the issue.

I'm going to start at the basics and work my way through again. I know I have a good alternator. I'm going to confirm the battery with a load test. After that, I'll check the voltages on the multi-pin before reinstalling the alternator. Then it's belt slippage, then voltage and continuity tests, then relays.

If the Jaguar gods are kind, it's a battery with a bad cell that the voltage tested good, but fails under load and needs to be replaced.

 

Sounds like a good plan.

 

Booty:
I don't know how fresh your electrical engineering skills are, so a few reminders might help streamline the process and give you a chance to go for a victory ride before midnight. Remember that voltage sums around a circuit. So if your battery is reading say, 13.7 volts and the alternator terminal to the alternator case ground is 15.0, you have a 1.3 volt drop in the connections from the alternator to the battery. To find whether that is on the power or the ground side, or split between the two, use Brutal's test method- read from the alternator power terminal to the battery plus. Then the alternator case to the battery ground should be the difference between the 1.3 volts read earlier and the power side loss. If either the power or the ground circuits are more than ABOUT .25 volts, you should look there for a bad connection. The ground path is easy, but if your power side has a big voltage drop, it is obviously harder to find.

I agree that is would be good to figure out what is happening when you hear the "click". The radiator fans, the AC system, or one of the evap system valves come to mind. That may or may not be part of the root cause, since the battery sghould float most any power draw not great enough to blow a fuse.

Your headlights on high beam make a pretty good load test at idle, meaning they draw about 10 - 15 amps, which is about what an alternator should do at idle. If you have a load tester, great, otherwise, turn on the headlights and measure battery voltage with and without the car running.

 

Alternator tested good, battery load tested good, eventually found the problem and fixed it. Voltage is now at 14 with brights and AC on. Everything else is perfect. So what was the culprit?!?

Drum roll please. . .

dubadubadubadubda. . .

THE GROUND STRAP!

Brutal is the winner with his prediction of:
It was burned up, corroded, and just plain nasty. Very cheap fix!

Thank you all so much. It's been a bit of a pain, I've gotten filthy, I've gotten bloody, but I feel like I've really gotten to know my car. This experience has had its highs and lows, but I guarantee I would have never had her running without this forum.

WOO-HOO!!!!

 

Thanks for coming back and posting the end result. It makes the thread much more complete and informative when people do this.

 

Do you mean the ground strap that goes from the battery negative terminal to the frame bolt in the trunk / boot ? Just to clarify. I had a similar problem, so I'm curious. TIA.

 

Jimmy, when I initially read Brutal's post, that's what I thought he was referring to also.

The actual ground strap in question is just like the one attached to the battery, but is located underneath the car. It's about a foot behind and a foot inside the passenger side front wheel. Very easy to find once you're under there and looking for it.

I ran into a problem removing it because (I believe) someone working on the tranny used a longer bolt than standard on one end. Once they finished work, it was impossible to remove the bolt due to interference. I had to saw the bolt off and replace it. Normally it would be a piece of cake to replace.

I'd recommend all do a quick inspection and a tightening or replacement if necessary. Very cheap and easy fix that could prevent a load of headaches.

 

A quick thanks for this extensive thread and for posting the resolution. I have been having some weird voltage drop issues ( mainly when electric fan engages ) and rough idle the moment after crank if a/c is on at startup. Wouldn't have thought to check the ground strap under the car so I will come daylight tomorrow, but I just wanted to prime your brains for help in case I find it intact.... Wish me luck!

 

My 1999 Jag is doing the same thing, the battery is good and I was told that the Alternator is good, yet the battery goes dead after running. I am inclined to believe that it is the alternator

 

I have the same problem. Wish I would have read this sooner.....I have already replaced the battery because the auto parts store said it had a bad cell. I haven't purchased an alternator yet (thank goodness). I will be checking the ground strap tomorrow.

 

My 1999 XJ8 had the battery loosing power and it tested good, there was also an odor comming from the engine compartment, auto zone said it was the alternator, but a shop said the alternator was good, it ended up being a double threaded stud that is under the right hand side of the cars wheel well, it apperently connects the battery to the fuse box or something like that. It was a real simple fix. The part eas threaded on both ends and was about 2/3 inches long

 

I'm having the same issue with my 1994 XJ12. I replaced the alternator 3 months ago and I have a brand new battery. I just got a decent amount of work done on my baby & now after getting it back for 5 days, the voltage went kaput. Trickle charged & was at a solid 14 & didn't faulter for a good 3 hours with lights & heat full blast. As soon as I took it to Advance Auto & they ran their test, it shot down to 12.3 volts & went downhill from there. I'm stymied & this happened a day ago, alternator, fuse or relay? Please help.

 

I had the same issue but it was funny I took both unit alternator and battery in the battery would charge but would not hold a charge it was considered a bad battery also I noticed I had a lot of corrosion on my my cables not to much but enough to want to be sure the thing about the car is if you don't use the correct battery I was told by Colorado springs jaguar that the car electric can be damage also don't put things in your cigarette lighter like power inverters HINT check your lighter socket if you did i found it funny when I did that to my jaguar that's where the short started and your warrenty appartently does not cover that and in your maunel it also tells you not to do that so dont do it or you will have the same issues just saying lol its possible not all consumers think about those things lol