Bit of a fun went to start my car yesterday and battery was flat. Charged the battery up and started it and wasn't charging so checked and the alternator exciter wire wasn't live so I lived it up and started charging. I went to turn it off and won't turn off so stalled it and re started it and it's charging now but won't turn off. So I removed the exciter wire off and then it turns off. Sounds like it's back feeding the ignition system but could this be Down to a faulty alternator ?

 

It's as that live is powering the ignition, as you suspect. This will cause all sorts of problems, as well as draining the battery.

Martin

 

That's right so is this a faulty alternator ?

 

Silly question, but is this a new car to you? ie did this problem exist before?

On some ecu installs the battery charge light can back feed a part of the system enough for the main relay to stay engaged. The common solution is to install a diode in series with the charge light.

Rob,

 

No it's not a new car to me had it for 10 years but it's been off the road for 6 years it's been fine for about 2 months then did this so can I just solder in a resistor or a diode into the exciter wire and that should stop this

 

It might do, however if it was fine and now is not there is a problem somewhere. Especially if you haven't made any changes to wiring.

 

No nothing has been changed at all its got the mk5 fiesta alternator on it so do you think it could be the diodes that have blown in the alternator

 

When it doesn't switch off flash main beam or press the brake pedal and see if it goes off, mine has done this for about 5 years and has never ever flattened the battery.

 

Not sure will check tomorrow did you find what was up with yours was it the alternator

 

No, was told to fit the diode to the excite wire but the odd time it does it I press brake or switch flash main beam and off it switches so never bothered getting around to fit the diode. My mates zt cabrio does it too.

 

It will by doing what he has done, as power will permanently be supplied to it, it will also cause other problems. The solution is to sort the underlying problem, typically the wire breaks, so it needs rewiring.

Martin

 

Had this very recently myself.

 

What was it on yours

 

I've got the same issue on the Orion...
Diode now sat here waiting to be fitted...

If I press the brake pedal and switch engine off its fine, if I don't press the brake pedal it runs on with battery light lit up...

Mentioned it to my mate that mapped it the other week when we went Oulton Park...
It's just one of them jobs we've never got round too...

 

All these random ways to turn the car off make me laugh. Although, I have experienced similar weird issues myself. On my old ERST a faulty turbo timer install meant that if I slowly turned the engine off through the different key positions it would die, but if I removed the key quickly it would run on Even worse than that was the period it went through where it wouldn't start unless the drivers door was open

Lee

 

As Rob says above, current feeding back.