Mercedes-Benz W123 alternator not charging
Mercedes-Benz W123 alternator is not charging: where is the fault?
Measure the voltage with the engine running and the lights on: about 14 V is fine, below 13 V points to a charging fault. First check the earths: from the alternator to the engine and from the engine to the body. After that check worn brushes, the voltage regulator and the connectors of the alternator wires. A faulty rectifier diode drops the voltage under load.
Why does the W123 charging light not come on or glow dimly?
The bulb of the light may have blown. The light is switched through the regulator and the brushes, so worn brushes or a fault in the regulator can leave it dark. The alternator does not start charging if the light does not work. A dim glow often points to a diode fault or a poor earth.
How do I replace the regulator and brushes of the W123 alternator?
The regulator can be replaced without removing the alternator; it is held by two screws. The brushes are replaced at the same time. If a brush has had time to wear the slip ring, that is renewed too, and it is worth replacing the bearings at the same time. If the fault returns after the renewal, the whole alternator may be finished.