There is a lot on the board about charge light always on but I can’t find my problem that my 2007 3.0 S Type battery charge light won’t come on so starting this thread.

The battery charge light does not light key on, engine off. Also does not light engine on and alternator not charging.

I’m not sure how long the light has been off because I don’t drive the car much but it surely was not coming on while the battery went flat. I found the alternator was not charging even though the charge warning light was not on when I got the car started again with a charged up battery. I assumed the light would start working again when I replaced the alternator.

What I assume is the original alternator was replaced with the same part number, 2R83-10300-AB. The replacement even had other printed numbers on the sticker match. The replacement charges the battery fine but no charge light, The charge light does flicker about a tenth of a second when the ignition first turned on, you can see if you don’t blink.

I have found that after disconnecting the positive battery cable the charge light will flicker once the first time the ignition is turned on like the original installation. I also found that with the low tension leads disconnected from the alternator that the light remains lit with the ignition on (interestingly the radiator fan comes on after a bit then and stays on for a bit after the ignition is turned off)

The only thing I can offer that changed in the electrical system is that I put in an AGM battery in 2018.

Can anybody help me diagnose the issue?

Attached video shows charge light blinking on after positive cable disconnected and replaced.

 

I wonder if this is an issue related to the internal resistance of the battery?

AGM batteries have a very low internal resistance compared to wet cell batterie, it is possible that the electronics in the s-type need this higher internal resistance to operate the battery charge light?
With your car I guess the only way to tell would be to try a wet cell battery and see if it sorts out the problem.

Mellow

 

Thanks for the comment Mellow. Failing any other options before following the wiring to the devices directly connected to the alternator, the ignition switch and ECU, I will surely rule out the AGM as the problem.