I have a 2004 1.8 TDCI

the battery light iluminates when driving (normally after about 30 minutes from start up)

If you switch off the engine and start it up again the battery light goes off.

the alternator has been changed but the problem still happens.

Any suggestions would be great.

i would start by checking that all the wireing and earth points are good and sound.

Hi,

My son had a similar problem with his 1.6 T reg focus, but the battery warning light would come on after about 15 seconds. After trying another battery and alternator we finally traced the fault to a break in the small red wire from the alternator to the underbonnet fuse box, F10 if I remember correctly.

As your light stay off for much longer it may be high resistance in this wire or a tiny break that makes and break contact.

John

PS have you checked the aux belt tension.

The belt tensioner is the automatic type and the tension is fine.

You are probably correct about a broken wire switching the light on, everything else seems to work and the engine starts fine.

although I have noticed with the dark evenings sometimes when the headlights are on the instrument lights pulse from dim to bright but it only happens occasionally while driving.

I will have to check the wires.

The belt tensioner is the automatic type and the tension is fine.

You are probably correct about a broken wire switching the light on, everything else seems to work and the engine starts fine.

although I have noticed with the dark evenings sometimes when the headlights are on the instrument lights pulse from dim to bright but it only happens occasionally while driving.

I will have to check the wires.

Hi

I know this thread is old, but I have this problem and I wondered if the fault was cures?

Thanks in advance,

Andy