Hi we have a ford focus cmax 2.8 diesel and battery light staying on after fitting new alternator how do I turn it off?

When car is running battery light comes on, when take battery leads off cars still running how do I turn light off thanks for reading

Never take the terminals off when the car is running. The ECU on your car can be fried.

Did you connect the 3 or 4 wire connector at the alternator? Yes, see a mechanic and get the voltage out of the L terminal of the alternator checked. If it is showing ground (or zero voltage) when the car is running, replace the alternator. No, connect it and see if the light goes off.

The battery light is indicating some sort of problem with your charging system. Maybe you should take the car to a REAL mechanic and have it checked out.

Taking the battery cables off while the motor is running can fry all of the modules and computer!
Check the fusible link for the electrical system to see if it's blown. It's located in the engine compartment fuse box and is one of the bigger fuses.
If the fusible links are good go to an auto parts store and have the battery and alternator tested. It's a free service. The rebuilt alternator may be bad right out of the box so you need it's output tested.

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