Sign in to follow this  
Mark Hyde

Battery Light

Recommended Posts

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.  

Share this post

Link to post
Share on other sites

Hello Mark,

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

Kind regards,


Share this post

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this