2.0 Zetec mondeo (51) battery light stays on

[Pete Cash]

Anyone help? Battery light comes on after c10 secs & stays on, then heated front screen doesn't work. Everything else seems fine, alternator charging battery fine (had this problem for 10 months). Ford want £40 just to hook up the diagnostics !
Any ideas?
Thanks

[GreenV8S]

The no-charge warning light indicates that there's a voltage difference between the alternator and the switched ignition circuit. This could be because the alternator isn't charging any more. You can test that by measuring the battery voltage with the engine running and confirming that it's above 13V.

If so check the alternator output voltage, it should be close to 14V. If it's higher than that it is over-charging (implying the electronics module has failed or the reference wire to the battery has failed).

[Pete Cash]

Ok thanks for reply - I already know the voltage is good at the battery, having checked this before, so will check the alternator output later. You mention the reference wire to the battery - what / where is this? I'm sure I've read somewhere else about a similar problem on a focus being down to a broken wire?
Thanks

Pete.

[Trooper2]

Here is a typical Ford alternator circuit if that helps.

[Pete Cash]

Thanks, I'll print this off & see if it leads me to the answer.

Pete.