2003 Jaguar S-Type 3.0 v6. Vin: M88734
Charging light came on after replacing the alternator with an oem remanufactered replacement. I've also replaced the serpentine belt and idler pully. I've tested the voltage and when the car is off it reads 12.6v and with it running 14.1. Battery is fine. Could it still be a bad alternator. I'm also wondering if there's a high output alternator I can install the factory voltage regulator in because I'm running 2 2500 watt amps in the boot with a 5000 watt capacitor.

 

The $64,000 Question(s):

Why was the alternator replaced? Was the light illuminated with the previous alternator?

If the fault is new, that would point to one of two things:

1) The new alternator is bad from stock
2) Something was disturbed during the installation, such as a connector that didn't get fully seated.

If you still had the fault with the previous alternator, I'd temporarily disconnect all of that extra audio equipment for troubleshooting. Don't just shut it off, but pull the fuses and unplug that massive capacitor. There's no telling how that stuff is interacting with the stock charging system.

 

The fault showed up after the new alternator was installed. I had both my battery and alternator tested and was told both was good. There's no CIL or DTCs and I could tell the difference right away when I started the car up with the new alternator, my lights barely dimmed at all.(I think I need a bigger alternator or an extra battery). I replaced the stock 120 amp alternator with a 136 pure energy oem replacement. The old alternator was all grimy and nasty looking.

 

I've checked the grounds in the boot and under the wheelwell. Is there supposed to be a second ground underneath of the battery? I'm gonna try switching the voltage regulator from the old alternator to the new alternator. If that doesn't work I'm just gonna send it back and get a new one.

 

Was it doing the same thing with the old alternator?

In my dim distant memory I think I can recall a fault with the wiring loom behind the front bumper causing this exact fault.
There was a known problem with the wiring ribbing through on early cars in this area, however I thought this was sorted out before 2003.
Mellow

 

Not trying to bust your butt, however you still haven't explained why you replaced the previous alternator. Reading between the lines, was it because you wanted something more powerful than stock for running your audio system? Some more details will help us understand exactly what is happening. And once again, I HIGHLY recommend disconnecting all of your audio equipment for troubleshooting, to rule out any adverse effects from those components.

This is the new alternator and same battery? The new alternator may test "good" if all they're looking at is normal charging system stuff like output voltage. The alternator's internal regulator, unfortunately, may not be communicating properly with the rest of the car, and thus is giving you the battery light. Once again, reading between the lines, you seem to be aware of the need for an OEM regulator. Most aftermarket regulators will not communicate properly. Who knows what is actually installed in the new alternator, despite it being an "OEM replacement".

I wasn't aware of different output options being available. And it also makes me wonder exactly what is the difference between the 120 and 136 amp versions. I bet most of the alternator is the same physically, but with a revised regulator to tweak the output a little bit higher. But if Jaguar never offered a 136 version, this regulator may not really be able to communicate like an OEM unit, and so you get the battery light.

 

There are a number of threads that aftermarket alternator do not have the correct internal control module (ones made by Denso) and the light will stay on, when there is no problem with the system at all. I have been lucky on some manufactured units and had no such problem.

Tom In Dallas/Plano
05 S-type 3.0 120K

 

I'm just going to take the alternator I took off to the repair shop and get it repaired for $40