Ford Focus battery problems
I just changed my alternator because it wasn't charging my battery. The problem is my battery light is still on, check battery showing healthy 12.5v it is the right battery. The alternator charges it at 13.8v it does go up very lightly when revved, I have taken the plug off the alt and at the time made no difference to the voltage.
But taking fuse 10 out in engine fuse box the charging goes up to 14.2v, so to me it shows I need to replace the red wire from the alt, but not 100% sure.
It would sound as though your battery and Alternator are both working okay. If as you say your battery is showing 12.5 v then with the engine running and measuring at the battery the voltage would not exceed 13.8v and may not even reach that.
The alternator decides what voltage is required dependant on the battery voltage.
So if the battery voltage is low then the Alternator will increase its output.If the battery is fully charged then it will reduce its output . There is no need to replace the red wire.
You may want to try resetting the ECU.
Disconnect the battery.
wait a few minutes.
Reconnect the battery
DO NOT switch anything on at all.
Leave for 15 mins.
Restart the engine.
The alternator decides what voltage is required dependant on the battery voltage.
So if the battery voltage is low then the Alternator will increase its output.If the battery is fully charged then it will reduce its output . There is no need to replace the red wire.
You may want to try resetting the ECU.
Disconnect the battery.
wait a few minutes.
Reconnect the battery
DO NOT switch anything on at all.
Leave for 15 mins.
Restart the engine.
Answered by Alan Ross on
