Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Alternator

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All Volkswagens are equipped with either a Bosch or Motorola alternator. The voltage regulator is mounted on the back of the alternator housing and includes the brushes. No adjustments are possible but the regulator can be replaced separately.

ALTERNATOR PRECAUTIONS





Always disconnect the battery cables when removing or disconnecting the alternator.
 
Disconnect the battery cables before using a fast charger. The charger has a tendency to force current "backwards" through the diodes and burn them out.
 
Never disconnect the battery cables or alternator while the engine is running.
 
Do not attempt to polarize an alternator.
 
Never reverse battery connections. Do not connect the battery in series with another without disconnecting it from the charging system.
 
When jump starting from another vehicle, try to avoid running the other vehicle's engine. Do not allow alternators from two different charging systems to be running and connected with jumper cables.
 
Do not ground the alternator output terminal.
 
Disconnect the battery cables before using an electric arc welder on the vehicle.
 

TESTING



There are several possible ways in which the charging system can malfunction. The first thing to do is to see if the discharge warning lamp on the dashboard illuminates when the ignition switch is turned ON . If it does not, check for blown fuses, a burned out bulb, or bad connections.

If the warning lamp does light with the ignition switch ON , but stays on with the engine running, check for the following:



Proper electrolyte level (specific gravity) in the battery
 
Loose or missing alternator belt
 
Loose or corroded battery cable
 
A blown fuse or fusible link
 
A shorted or open wire
 

If everything checks out OK, but the charge lamp is still on, the alternator itself is probably to blame. This does not mean the entire alternator needs to be replaced. Many times the voltage regulator may be faulty and cause a no charge condition. Check the charging system by performing the following tests.

Current Drain Test

Perform this test first to be sure there is not a shorted circuit or component which is constantly draining the battery.

  1. Turn the ignition switch to the OFF position. Make sure all electrical accessories are OFF.
  2.  
  3. Disconnect the negative battery cable. Connect a test light between the battery cable and the battery post.
  4.  
  5. If it lights up, something is either switched ON, or a wire/component is shorted and is draining the battery. To isolate the problem circuit, remove the fuses from the fuse/relay panel one at a time until the test light goes out.
  6.  
  7. Repair or replace any wires/components as necessary.
  8.  

Alternator Output and Voltage Regulator Test
  1. Connect an alternator/regulator tester according to the manufacturer's instructions. Volkswagen recommends a Sun VAT-40 or 60 model. If this equipment is not available to you, further charging system testing should be performed by a repair facility which is properly equipped for charging system diagnosis.
  2.  
  3. Start the engine. Make sure all electrical accessories are OFF.
  4.  
  5. Run the engine at 3,000 rpm, then adjust the load to the maximum ammeter reading (do not allow the voltage to go below 12 volts). The maximum ammeter reading should be equal to the alternator rated output minus 16-20 amps. If the reading is below this specification, replace the voltage regulator and retest. If it is still too low, the alternator is defective.
  6.  
  7. Leave the alternator/regulator tester connected (a voltmeter connected to the battery terminals and set it to the 20 volt scale may be used instead of the alternator/regulator tester). Make sure all electrical accessories are OFF.
  8.  
  9. Run the engine at 3,000 rpm. The voltmeter should display between 13.5-14.5 volts.
  10.  
  11. If the voltage is not as indicated, the voltage regulator is probably defective.
  12.  
  13. Remove the alternator/regulator tester. Repair or replace any components as necessary.
  14.  

REMOVAL & INSTALLATION



See Figure 1

Before purchasing a replacement alternator, read the specification plate on the housing. The number 14V will appear to indicate maximum voltage rating. On the same line will be two more digits followed by the letter A . This is the maximum amperage output. Be sure to purchase an alternator with the same rating. The regulator can be replaced without removing the alternator.

  1. Disconnect the negative battery cable.
  2.  
  3. Disconnect the wiring from the alternator.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Make sure the battery cable is disconnected before removing any electrical connections from the alternator

  1. Loosen the bolts, then remove the belt from the alternator pulley.
  2.  
  3. Remove the mounting bolts and remove the alternator.
  4.  

To install:
  1. Position the alternator and install the mounting bolts.
  2.  
  3. Tension the drive belt, then torque the bolts to 20 ft. lbs. (27 Nm).
  4.  
  5. Connect the wiring to the alternator and the negative battery cable.
  6.  
  7. Start the engine and check for proper charging system operation.
  8.  

 
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