I have a Jaguar XJ6 4.0 sport 1995. I was driving the other day and the battery light came on and the battery meter was low. So I stopped and the car would not start again. So I called my breakdown company. The breakdown guy come and checked the voltage off the battery. It was showing 11 volts and when revving the car it never went up. Does this mean the alternator is not working or should I check the alternator fuse or realy ?. I do not know the location of the alternator fuse or relay if anyone knows it would help ?. I did not want to buy a alternator and its not that. Also One of my fuses keeps blowing which I think is the fuse for one of the headlights. But this kept blowing before this fault occured. Any ideas would be most grateful ?.

Many Thanks
Mat

 

Its a simple circuit alternator terminates at the starter motor make sure its a good connection, fuse #1 5amp right hand engine bay hot when engine is running

 

I believe its this fuse that keeps blowing. I tried to put a higher fuse in but then the wiring near the windscreen started smoking and smelled of burning. So I just put the blown fuse back in. If the alternator is faulty would it keep blowing this fuse. I do not want to buy a new alternator and it does not solve the problem.

 

Mat:
"I do not want to buy a new alternator and it does not solve the problem."
Right! You want to diagnose, not exchange parts! So, remove either lead from the battery. Then remove the big wire from the alternator. With a ohmmeter, test the terminal where the big wire was connected, to ground. If you have a low resistance {less that 10 ohms,) you have found your bad alternator.

 

The same fuse feeds ignition-switched power to 7 places, including the alternator and the RH lighting control module.
Fuses of specific ratings are fitted to protect the wiring from damage, or even a fire, in case of excessive current flow due to a fault. You have proved what happens if the fuse does not blow!
I suggest it would be prudent to investigate the wiring where the smoke escaped. If that is ok then disconnect the (smaller) alternator wire and try a 5A fuse again. If it does not blow suspect the alternator.

 

Yeah, I agree with Rads. I did not look at the specific fuse in question- Indeed, for that one you should take off the small wire then test the small terminal to ground.

 

I have removed the alternator ready to fit the new one. The guy that took it out of the car for me never wrote down where the black wire goes on the alternator. I wondered if it was the connector at the top of the alternator with the bolt on top of it. Or it was the connector on the far right off the alternator opposite the red connector ?. Any ideas would be grateful.

 

Have just changed the alternator and the battery is still not being charged. I wondered if anyone could point me the right direction for a picture of the wires which go to the the alternator and the right locations for them ?. The person who took the alternator off the car cannot completely remember which wires go where. Maybe there in the wrong place.

 

I noticed in the boot that the far right relay is missing from the fuse box. I appears to have wires underneath. Any ideas what this relay is for ?.

 

N = Brown.
B = Black.
W = White.
U = Blue.

From the MY96 electrical diagram - I think the 3.2, 4.0 and 4.0 S/C are all the same. I can recommend buying the X300 workshop DVD with all the diagrams from Jaguar/Daimler Heritage Trust - it's excellent.

 

I have a Jaguar XJ6 X300 4.0 sport I fitted a alternator as i suspected the alternator was faulty. Because the battery was not charging when driving. I fitted the second hand alternator and the same problem remained. So not sure what else to check. I checked the voltages at the battery and behind the alternator which was:- Voltage at the battery when car is running was 11.73 volts. Without car running 11.97 volts. From back of alternator its reading 12 volts without car running. Which must mean the wiring to the battery is ok. Reading 11.71 volts from back off alternator when car is running. Any suggestions on what to check would be appreciated ?. I was wondering if the battery was faulty maybe but it seems fine and holds a charge for a while before going flat even when driving even though alternator is not charging the battery. Also was thinking maybe the alternator is not spinning fast enough to create the right voltage. Not sure im confused about the whole thing. Mat

 

Its been some time since I was under the bonnet of an X300, but alternators are alternators, basically.

There is a small wire on the back of the alternator, usually a plug in terminal. This is known as the "excitor" wire in auto talk. Unplug this wire, plug the Red wire of your volt meter into that wires plug, and the Black wire of the meter to ground. Turn ON the ignition, and you should have battery volts in that wire.

On most systems, that volts is supplied via the Red charge light in the instrument cluster, and NO volts in that wire is "usually" a blown bulb, and the alternator will not excite, and that means it will NOT charge.

Older Lucas/Bosch/Motorola alternators had the ability to "self excite" if spun fast enough, BUT, I doubt the Hitachi has that ability???

Now the fun begins, the X300 has many "Ignition Relays" all over the car, and one of them would be the feed for that system I RECKON.

If it were mine, I would take your OLD alternator to any half decent Auto Electrician, and ask him to test the thing. He can do that on his test bench. That will at least confirm OK/Bad of that unit. If it test OK, then the car has an issue as I mentioned above.

 

Is there anyway you could run a wire directly from the back of the alternator to the battery just to check to see if that works ?.

 

I also suspected that the alternator is maybe not spinning fast enough to create the right voltage. It just seems strange that two alternators have the same voltage readings as each other.

 

Not sure on that live wire on that cars system. It may be OK, but it is only an excitor circuit, that cuts out when the light goes out, and the excitor diodes take over, and a constant live feed could damage stuff.

Not spinning fast enough sounds odd. It is belt driven, and unless the rubber of the crankshaft front pulley has de-lamentaed and the drive section is slipping on the centre section, the speed is the speed. If that rubber was loose, then the water pump would also be spinning slower than designed and the engine would be overheating?.

Check that wires volts first. If its got volts, then other things are at play, and the alternator testing would be #2 on my list.

 

Hi Mat,

I have merged your three threads into one so all your posts and all replies will be together. It gets very confusing when the same issues are being discussed in multiple threads.

Your voltages all seem quite low. According to the X300 Workshop Manual, a fully-charged battery should measure 12.7V without the engine running. 12.11V represents a 50% charge, and 11.74V represents a 25% charge. A common reading I see on our battery without the engine running is 12.5V. Temperature must be taken into account, but it appears your battery is less than 50% charged.

Also according to the manual, the nominal regulated voltage from the alternator should be 14.4V at 25 deg. C. In operation, the voltage will vary between roughly 13.7V and 14.8V, depending on engine rpm. Are you measuring the alternator voltage only at idle, or at a higher rpm such as 2,000? How is the tension on your alternator belt?

I'm not an electrical expert, but when our '93 has had battery charging issues, cleaning all the relevant ground points and battery power connections has usually solved the problem. Some of the critical points include the battery terminals themselves, the negative battery-to-body ground, the engine ground strap, and the three bulkhead connections. The fuseboxes are all daisy-chained together, so corrosion or looseness of any of their battery power connections can cause problems. You can see all these connections in the schematics in the X300 Electrical Guide, and you can download the version for your model year here:

JagRepair.com - Jaguar Repair Information Resource


The video below may give you some ideas of tests you can conduct to narrow down the problem:



Hopefully one of our electrical gurus will correct any of the above.

Cheers,

Don

 

I suspect the pulley because all three alternators I have tried have the same voltages at the battery and at the back of the alternator. I checked the voltage on the back of the alternator with all the wires still connected to it. Which I did not think would make a difference or do I need to disconnect all the wires and clips before checking the voltage from the rear of the alternator ?. Also when you rev the car the voltage from the rear of the alternator still remains the same. Im not sure if the voltage should change when you rev the engine anyway.

 

In response to Don B reply. The belt is tight and also the voltage remains the same on the back of the alternator when idling or revving the engine. This is why I suspected a faulty pulley. All 3 alternators I have tried the voltage has been the same at the battery and at the rear of the alternator.

 

What fault do you suspect the pulley has? The chance that the pulley is slipping on the belt and not making a loud whine is infinitesimally small.

 

I'm not sure what the problem with the pulley is. But if the voltage on the back of all 3 alternators is the same when the car is idling and off. Also when the car is revved. Also the voltage at the battery is the same when idling and switched off. It make me think its a belt issue or pulley issue. I'm totally confused with the whole thing.