Hi all, I'm after some help with my ford fiesta it's a 59 plate mk7. Bit of a amateur at repairs but have had help from a mechanic friend.

One cold morning I couldnt start the car sounded like a dead battery, called RAC out I suspected faulty alternator as it's been taking a few extra seconds to start recently and the battery is less then a year old. 

Rac, myself & my friend confirmed the voltage from the alternator was at 10/11v to the battery. Too low to charge the battery. Replaced the belt and alternator for a new one... BUT it's still reading 10/11v.

 

I've read online that it could be a fuse but I'm having a hard time locating what fuse or fuses I need to be checking. I've also  checked earth and splits in cables. 

 

No warning lights on dash.

 

Can anyone help please? Does anyone know what fuse I need to be looking at or cable etc?

 

Thank you 

 

 

Hi Tom, first thing to do is pull the little 'Smart Charge' connector out of the side of the alternator.

Start the car and measure the voltage at the battery terminals, with the engine at about 900 RPM the voltage should be about 13.6V or even slightly more. If it is then good and you can say the alternator is most probably ok.

Let me know the result and I'll tell you what to test next.

Hi @unofix I have done this and I'm reading nearly exactly the same as I was with the old alternator.

 

The new one is reading around 11v. 

 

Thank you for your help

 

Tom 

If you are reading only 11V with the smart connector disconnected then your alternator is faulty - no doubt about it.

With the smart plug removed the alternator should default to standard charging as a fail safe, so it looks like your replacement is duff !!

If it was brand new then it will of course still be under warranty, and if it was only a refurbishment then the fact that the smart charge is faulty is no great surprise.

Thanks @unofix I'll double check that I've pulled out the right bit (smart charger plug)  and test again tomorrow as I'm now doubting myself pulling it out.

 

I'll let you know.

 

Thanks again

Smart charging connector

Hi @unofix have done what you said and I can confirm the alternator is putting out 14v after removing the smart charge socket.

 

Am I right in thinking theres also a fuse for the alternator?

 

Really appreciate the help

 

 

2 hours ago, godsgamer said:

alternator is putting out 14v after removing the smart charge socket.

That's good news, so you can probably assume for the moment that the alternator is working correctly.

There is a "smart" charge feed back fuse (sorry don't know the fuse number) I believe it is a 7.5A, but I don't expect it to be blown.

What you need to do now is check the wires and resistance of the "Smart charging" plug. Is yours a 2 wire or 3 wire connector ?

Using a multimeter on the DC volts range test each of the wires the plug. One of the wires should measure about 12V positive with respect to the battery negative terminal. Once you have found the positive wire in the smart plug you need to put your multimeter on the Resistance range. Measure what the resistance is between the positive wire in the smart plug and the positive terminal of the battery is. The resistance should be less than 2 Ohms. I expect that when you check it you will find the resistance to be much higher, if that is the case then you have found the fault. Let me know what the results are and I will try and advise what to do next.

In the mean time leave the smart plug disconnected from the alternator, and it will charge your battery the same way a conventional alternator would. This is only a temporary measure and not a 'fix'.

 

On the Mk7 you will probably find the 2pin connector has only 1 violet wire. It's a linbus wire. I had a transit that wouldn't charge after a flat battery. For some reason it wouldn't charge until the battery was fully charged again with a external charger. So charge it fully  and test voltage again.