Hi all,
My XJ6 S3 had the battery light come on with voltmeter needle at about 11v while running. About 300 miles ago I replaced the alternator, and in the spring I put in a new battery. I checked battery for bolts and it’s at 14 volts (tight connections on + and -). Alternator connections are tight also. Cleaned up grounds also. I’m at a loss for what to check next.
Thanks in advance,
Alan

 

A little weird.

At 14v the alternator is obviously fundamentally working.

Since you've checked the wires and connections I have to think there's a problem with the alternator

Does the light stay on even with the ignition off?

Will the light turn off if you rev the engine up?

Cheers
DD

 

 

 

what alternator did you buy? I replaced the original Lucas alternator in my 1984 with a more amps is better GM alternator, and I was never happy with the GM alternator. Fortunately I kept the old Lucas and problem solved.

most likely it is the alternator.

 

I saved the Lucas alternator as well, however the voltage regulator in it was faulty. I’m going to try to ground it better. I’ll try that jumper to the battery ground and see what happens.

 

Mike Martinez in California rebuilds all sorts of classic car Lucas generators and alternators. Star Auto Electric is his business.

Based in my experience, I prefer the Lucas, it seems to be better calibrated to the XJ-6 gauge.

 

I sure dunno know. English volts and amps are the same as American !!!

But, a well rebuilt Lucas will trump a poor Delco.

OTH, many Jaguars are doing well with either.

My lump excels with its 140 Amp Delco. A really large unit up top, right front. Serpentine belt driven a sure positive.

A while back. I created a patch cord. enabled my HF VOM to connect at the cigar outlet. Real volts I real time at various loads and RPM's. One of my better ideas. Convicted a battery and acquitted an alternator !!

VOMs are great !! All three of my cordless driver/drills were flat when needed !!
A session on their chargers revived two.

The third, a slick angle drill, zip!! Oh me, a charge session got only 7+ volts. 18 or near about needed. Back to the charger. Hope for 18 faint ! it may leave

Carl… …. ...

 

You're right, Carl.

There's nothing inherently sub-par about Lucas alternators. They're as good as any other. The problem, at least on Series III cars, is that Jaguar specified (or settled for?) a unit that was just barely up to the task in terms of output.

Once any alternator has been rebuilt...Bosch, Lucas, Delco, Motorola, Denso, whatever...future performance and longevity probably has more to do with the quality of the rebuild than the original make/brand.

Cheers
DD

 

Calibrated to the gauge?

The voltmeter does have an adjustment to correct for a too high or too low reading.....but it has no way of knowing if the volts are being generated by a Lucas alternator or Delco or whatever. It just reads voltage. The alternator and voltmeter are not calibrated to each other.

Cheers
DD

 

Yup!!

My Jaguar's guage reads the same with the Delco as it did with the Lucas. By nature the gauges are a bit slow on the uptake. And, for me more of an indicator than true guage. Hence, my patch cord device to verify from time to time.

And, when things electric go odd, go the ground route. Not forgetting the down and under one at the engine transmission joint. Very important.


decades ago, I was messing with my Webber equipped turbo Corvair. Lots of effort at the very tunable Webber to correct a flat spot in acceleration., Not getting anywhere. then my bare elbow touched the nearby battery ground cable. HOT!!!! Not good, much resistance, poor connection! Indeed, it had one of those "Mickey Mouse"
clap on the at the battery - post. Should 've dumped that a long time ago. My shop wall yielded a much better cable. Installed, cleaned at both ends. !!!! Flat spot gone.. revved like a champ...

Carl

 

Had this same problem with the Silver Six (earlier '85 SIII). Replaced the big spade terminals at the alternator with ring terminals and the problem disappeared.