Battery light issue

Hi All,

New on here so be gentle! Have a issue with my 300tdi 90 battery light on the dash. It started a couple of weeks ago on Salisbury plain after some snowy wet lane crossings, ended up with a flat battery due to a non functioning alternator. Have since replaced the alternator and fitted a new battery for good measure... but the dash battery warning light remains on when running. Have checked with multimeter and the new alternator is charging the battery giving 14.5v when running at both the alternator and battery terminals. Believe there is a wire between the dash and the alternator, perhaps this is shorted? Thoughts more than welcome.

Many Thanks,

Josh

There should be a thin brown and yellow wire that attaches to the rear of the alternator, have you forgotten to re-fit it, or has it become damaged? This is the trigger wire for the charging light.

https://www.google.co.uk/search?q=a...d=chrome-mobile&ie=UTF-8#imgrc=OUJtLwIJtBvjfM:

https://www.google.co.uk/search?q=a...d=chrome-mobile&ie=UTF-8#imgrc=VWGSFPBHM0UFdM:
Simplified diagrams of alternator set up.

The charge light has a diode in the wire - when you switch on the ignition it allows current to flow from the battery, via the ign. switch, via the light then the diode and onto the alternator field winding diodes - this gives the initial power to start generation, although most alternators will actually start without it, once the alt starts it will self excite via the field winding diodes from the main windings.

If your light is remaining on it would make me think that there is a path to ground after the light that is running it like any other lighting circuit, or there is an issue with the alternator field winding diodes or you have connected it to the wrong terminal.

Thanks all, going to have a look at it over the weekend. Will report back!