Battery Light

[Mark Hyde]

Hi There

I have an Audi A4 Cabriolet 2002 2.4, about a month ago my alternator broke and the battery wasn't being charged, i changed the alternator for a new one and the battery was being charged at 13.8v whilst the engine was running, the only problem was the dash board battery light was still constantly red. I have been driving the car now for a month with no problems, but the battery light has been red the whole time and is driving me crazy.

I have tried to fix it by checking that the alternator is grounded to the body, which it is. I have disconnected the Blue Exciter wire from the L terminal on the alternator and checked for 12v coming down the blue wire when the ignition lights are on but get 0v, I believe i should get 12v so assume i may have damaged the blue wire/connector, but when this blue exciter wire is not connected to the alternator the battery is not being charged only 12.2v with engine running, as soon as i connect the blue exciter wire to the alternator the battery is being charged at 13.8v with engine running, so i assume the blue exciter wire is sending a message to the alternator to start charging the battery.

Has anyone got any ideas why the dash board battery light is constantly RED, is there a fuse in the circuit on something.  

[Magnet]

Hello Mark,

In my book 13.8v is too low, and you should be looked not at around 1v more than that. 

Kind regards,

Gareth.

[Magnet]

Typo:- ...should be looking at......