Charging light on 87 XJS V12 Coupe

I have recently developed a problem with the charging light on my 1987 XJS V12 Coupe, when I start the car up the voltage goes from 12 volts to 13.8 volts immediately but the charging light stays on then slowly dims and goes out after 20- 30 seconds, I am wondering where the problem lies, is it in the regulator built in the alternator or another circuit somewhere else in the car? TIA Geoff

Hi Geoffrey,
This is normal, there is no problem in my humble opinion.
Cheers Bruce

I agree with Bruce. Mine does the same thing. Not a problem.

Mine did the same.


Mine was an '88. It had two charging system lights. One was a typical ignition/charging light (with a battery icon as I recall). It extinguished quickly. The other was an overcharge warning light (with a lightning bolt icon) which extinguished slowly. I think your '87 would be the same.

Something like that. It was 20 years ago so my memory isn’t 100% clear.


Mine has both the ignition light (with a battery icon) and an overcharge light (with the flash icon) the overcharge light goes out immediately but the ignition light takes awhile, I never remembering it doing that before, but as the battery is charging I guess I have nothing to worry about but wonder why things changed (oh I know, it’s an XJS!) My 91 convertible does not do this it goes out immediately.

My 1988 does the same, but usually goes out after just 8 seconds max.

I wonder if it takes longer to go off if the battery is less charged up? If so, do you have a drain on battery like light left on?

Greg, that’s a great point, I don’t have a drain on the battery but I do drive it a lot of very short trips, I am going to charge the battery tomorrow and see if that changes anything, cheers Geoff BTW my 91 has a brand new 115 amp Bosch alternator, not sure what is in my 87 Coupe.

Greg, charged battery up no difference, I did actually time it took to extinguish and it was about 10 seconds not what I thought, also I have noticed it flickers while dimming it’s not a happy light.

Hi, once again i think this is normal. Seem to remember it being mentioned in the hand book.

Totally normal. Mine does the exact same thing. British.