The battery light came on on my friend's Ford Ka a week ago. Battery seemed to be fully charged at 12.5V, alternator was putting out 13.5V. (Battery light comes on if voltage drops below 13.8V.)
Jacked up the front of the car, took off the front wheels, removed the front bumper and plastic trim round the wheel arches. This was held on with a mixture of torx screws, phillips screws and white plastic clips (the clips can be squeezed with pliers to get them out without snapping). Once the bumper was off there was enough access to the three pin plug on the alternator to remove it by *gently* prising against the plastic clip with a flat headed screwdriver and sliding it off. The back of the plug had three wires - orange and red, blue and grey. The blue one was broken off tight against the connector for pin 2. The pins for the connector plug are numbered on the back and are:
Pin 1 = Alternator Feedback
Pin 2 = Alternator Load Request
Pin 3 = Reference Voltage
without the alternator load request pin connected the alternator converts to a conventional mode, not 'smart charge' although the other mechanicals of the alternator work fine.
Went to the Ford dealer and bought Ford Connect part no.1421293 This is actually a Ford Transit part but includes the same three pin connector as the broken one for the alternator, about a foot of wire and another type of connector that wasn't needed.
Back on the Ka, disconnected battery (-)ve, pulled back the black plastic around the wiring and cut off the old three pin connector where the wires looked less corroded, leaving a little bit of each wire free. Then cut the new part in half to get a new three pin connector with three wire tails that could be attached to the three wires on the Ka with wiring snap connectors. Noted down which wire went to which pin on a notepad for this bit to avoid mix-ups.
Electrical taped round the connectors and the top of the new plug where it attached to the alternator to keep water out and stop the problem happening again. The alternator now charges at 14.2V, battery light switched off. Took 1/2 a day to fix.
Paperfrogs
June 2012