940 battery light?

[svol]

Evening All, the battery light doesn't go out after starting. It stays on but not fully bright but it seems to get brighter as the revs build. Otherwise the car is running well. I've just changed the battery so all good there. Any tips or advice would be greatly appreciated. Many thanks.

[Rversteeg]

It seems your alternator is not charging anymore. If you measure the battery voltage, is it over about 13 V when the engine is running?

Probably one or both of the brushes at the rear of the alternator have worn out. Replacement is not too complicated and not too expensive (look for "voltage regulator").

[Forrest]

I agree this is probably a faulty alternator. However, it's important to appreciate that the no charge light on the dash makes its circuit to earth through the (thin) D+ wire connected to the back of the alternator. It goes out when the alternator is pushing enough current the other way up this wire to stop the flow of current through the bulb. If the bulb is dimly lit it means that there is still some current flowing from the bulb through the alternator. This is most likely due to the reason already stated, but could be due to another fault in the circuit.

The alternator relies on +12v from the battery via the charge lamp on the cluster through D+ to excite a coil to start the charging output. If you suspect this circuit is not working properly you can mimic the effect by attaching a wire to D+ and touching it to the battery positive long enough to get the alternator to start charging. For safety you can include a bulb in circuit to limit the current through this test wire.

What you probably don't want to do is go to the expense of replacing the alternator only to discover it's not working due to a simple fault with the exciter/warning-lamp circuit.

[svol]

Thanks for the advice, found a reasonably priced alternator and fitted it along with a new belt and all is good so far.