After low voltage on my 2003 S-Type 6 cyl 3.0 , I replaced the alternator with a re-manufactured Carquest "exact fit" alternator. The battery light remains on after starting even though voltage output measures around 14.5. After internet search, found comments stating that any aftermarket alternator would give this issue. The car has has no problems except the warning light staying on. there is no code and resetting does not eliminate warning light. I figured there must be a jumper or other modification to cause the warning light and wondered if anyone had an easy fix without having to buy a Jag alternator at 8x the price.
Thanks for your input.

 

The proper alt is a smart charger and changes voltage. Yours is not behaving the same so will not properly charge the battery and you also get the warning light.

The fix is to repair your original or use a correct equivalent (or a used one).

 

I think there's a fuse in the trunk. #26 Or #27.

Forum search this topic in the X350 section of the forum.

 

You'll be fine if you can live with the warning light, though you'll have lost its function.
Since you mentioned it is a reman, I'll assume you've turned in your original to avoid a core-charge and it is lost forever.

Your alternatives to extinguish the light, apart from sourcing a new OEM alternator that you already mentioned can be cost-prohibitive, include replacing the alternator with the proper one from a breaker, or, some have reported fitting the control electronics from the OEM to their aftermarket alternator and achieving success. I don't know if those bits are available from a breaker or eBay. Either way, you'll likely have to get your hands on an OEM alternator or some pieces of one. Meanwhile, the battery will charge just fine (although perhaps not "properly" as John says) and you can drive the car day-in and day-out with no issues apart from the warning light while you seek a solution.

I used such an aftermarket alternator for 2-3 years without any electrical issue before finding a replacement OEM alternator at a breaker for $70 some odd. Don't recall exactly when, but that one has been in service over 5 years with no issues, while the functional but problematic aftermarket is tucked in a box on the shelf for "next time." which will afford me time to have the original repaired at an electric shop.
One advantage in solving the problem sooner rather than later is you may be able to get your money back from the aftermarket one if you solve it during the warranty period....because it doesn't actually "work" in the sense that it was supposed to be a direct replacement.