Hi Fellow Jaguar fan and expert!
I installed a new alternator on my 1986 Jaguar Sovereign. Last time I drove it, the alternator gauge starting to acting up. It showed that my alternator was not charging, then after that the gauge showed that it was over charging at 14 volts. When the engine idle, the gauge shows lows and when I rev the engine it goes up to 15 volts.
Do you think it has to do with the internal voltage regulator? Is there a way to confirm without removing the alternator?

thanks

 

is the car a Series III body or a XJ40 body? The XJ40 body models started being sold in 1986 in Europe. Different electronics between both body styles.

 

It is a serie 3

 

Yes



Hmmmm.

I can't think of anything except a faulty regulator that would cause this. Low voltage could be a number of faults but going to 15 volts would be the regulator, IMO

Cheers
DD

 

Jean Pierre
The alternator should be holding a steady voltage all the way from idle to max revs. That is why alternators are so good compared to the old generators
You could cross check your dash voltage indication with a multimeter just to confirm the voltage variation.
I agree with Doug's diagnosis of a regulator problem.

 

Thanks, I purchased a new regulator. I will replace it

 

it is a pain to remove but it must be done to test it.
Just get a good alternator in advance, remove the old and replace with the new in the same session while everything is fresh in your mind. Save the old one for a spare.

try to find the alternator for the 12 cylinder Series 3, Doug knows the part number, it is a straight fit but has more power than the Lucas.

 

Before you start replacing things. Get a volt mater and check your voltage across the battery terminals and see if it matches your onboard gauge. A digital one that goes into your cigarette lighter may also give you a good reading.

 

I a time ago, I made a atch cord. connect my VOM to the cigr lighter outlet. slick. read volts in real time under varius loads and rpms.

Carlp