Vauxhall Vectra

[robert30]

The battery is flat and the battery light is on even when the ignition is not switched on. Is it the battery or alternator.

[Jay70]

Hi Robert,

Exactly the same thing happened to my wifes Escort. It was a short in the diodes in the rectifier pack on the altenator. I had to get an exchange unit which sorted it out. Just out of interest this is a common failure caused by jump starting another car with a flat battery with your engine running, as the current drawn from the car with the good battery is so high it damages the rectifier diodes.

To test disconnect the car batteries negative lead (if negative earth).Then diconnect theconnector on the altenator, re-connect the battery negative lead and see if ignition light is still on. If not then it is the altenator at fault.

Also on my wifes car the battery voltage was being dragged right down by the short with the altenator in circuit. So you could measure this before and after disconnecting the altenator as extra confirmation. When I asked a few self certified car experts they said they had never heard of the light staying on with the ignition off. They said it would only be on with the engine running but this off course is only true if the diodes are open circuit and the rectifier circuit is only half wave rectifing or not rectifing at all.

best of luck let us know how you get on

Jay