Voltage Regulator — Check (Mercedes-Benz S-Class W126)

Depending on which generator is installed, a voltage regulator is also needed. Since the regulator contains transistors and thermistors, it must be replaced in any case if it fails or breaks. The work described below must be carried out before simply replacing the regulator.

Before performing any checks on the charging system, make sure the battery is fully charged and all connections and wires are clean and tight. The belt must be tensioned correctly. When checking voltages, make sure the wires between the alternator, battery and ground wire are in good condition.

• Connect the voltmeter to the "B+" terminal and ground.
• Start the engine and maintain the speed at 3,000 rpm.
• Give the battery a load by turning on the low beam, fog lights and windshield wipers.
• Measure the regulated voltage for 30 seconds, which should be between 13.0 and 14.8 V. If this value is not achieved, then the regulator must be replaced and the test repeated. The transistor regulator is not adjustable.