The Jag just stopped starting. But would start with a battery jump. They said it was the alternator. Had that replaced for days ago. Today the car would not start again. It tried to turn over but just lost the power like last time and then nothin. WTF

Probably complete failure of the I/P dimmer

The charging system on your vehicle is computer controlled . The ECM - engine computer turn's on the battery light if it think's there is a problem . Sends a message to the instrument cluster over the class 2 serial data network . Have you had the vehicle checked for DTC's diagnostic trouble code's ?

taking the battery leads of a running alternator is one sure way of destroying the alternator
if you think a battery is dead you have it load tested and replaced if it doesn't meet the test
what you should be doing is taking the vehicle to an accredited auto electrician and having the battery load tested and the alternator and voltage regulator professionally tested for proper operation

Most likely the battery. Most auto parts stores will check it for free with the hopes that you will buy your replacement from them.

Check and clean the terminals then boost the car to start it after it starts. Well it's running take off the positive terminal if the car stops running the alternator is no good and you have to replace it.

you should check the voltage on your batttery when the car is running. If it reads about 13.5 to 14 volts, your alternator is doing it's job. If it's less, replace the alternator. If the alternator is ok, you have a power drain somewhere, you will need a proffesional to look at it.

Even a new battery will go dead if the car is running on the battery instead of the alternator.
Check alternator output.
First charge the battery up.
Then check voltage with a meter from Harbor Freight ($3).
Should be 12.5.
The start engine and rev it up.
Should go over 14.
But also clean and grease battery terminals, alternator terminals, and check engine ground strap.

your charging mechanism may ave gone bad or even your alternator. you can check those things out at autozone. they'll check it and i think it's free

Hi Clyde

Expect you have it running by now, as I see this was posted 2 March ?

If not......

Charge up your battery, and heavy discharge test, suspect you have short in the plates.

If OK, jump start with a set of proper heavy duty jump leads.

Good Luck !

A FixYa would be nice...Thank´s......John.

sounds like the starter has gone out. when tey go bad the will put a draw on the battery