The following covers the procedure for replacing the voltage regulator in VW Jetta models from 1980 through 1999. It's not possible to perform an adjustment on the voltage regulator in these vehicles. Therefore, if the regulator stops working properly, a complete replacement of the regulator is necessary.
Look at the back of the alternator to check if there's a cover over the voltage regulator. If so, it's necessary that you remove it. Place the screws and the cover to the side, as you need to replace them later. There's no need to disconnect any wiring from the regulator or the alternator before you remove the voltage regulator.
Use an appropriate screwdriver to remove the retaining screws that hold the regulator and the alternator together. Set these screws aside in a safe place so that you don't lose them.
Use a ruler that measures inches to measure the free length of the brushes on the regulator. Remember that new voltage regulator brushes are about 1/2 inch long. If the brushes measure less than 7/32 inch, it's necessary that you replace the regulator, whether it's working or not. If the brushes are too short, this could be the source of any problems you may have with the voltage regulator.
Install the new voltage regulator. Tighten the retaining screws to hold the regulator onto the alternator securely. If you removed a cover from the rear of the alternator in Step 1, you should replace it over the new regulator now.
