5.2 In-Vehicle Testing of Charging System

The tests described here will help determine the cause of charging system trouble. For the tests, the battery should be fully charged and the alternator V-belt should be tensioned correctly. If in doubt about either, test the battery as described in 4.1 Testing Battery, and adjust the V-belt as described in 5.3 Removing and Installing Alternator and Voltage Regulator. The charging system warning light should be operating correctly. All electrical connections should be clean and tight. Replace wires that are hard or cracked.

A general test of charging system output can be made with an accurate digital voltmeter. The most accurate testing is done using an alternator and regulator tester, such as the Sun VAT-40, that applies a high-current load to the alternator. Conclusive tests using this equipment can be performed inexpensively by an authorized Volkswagen dealer or other qualified shop.