Voltage Regulator

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Old Voltage Regulator

The other day my generator light came on and would not go out. I ordered a new voltage regulator and started to read the factory service manual about the generator and voltage regulator. There are some pictures of the new voltage regulator at the bottom of the page. I was lucky because for now the generator is just fine, my problem was temporarily fixed with the new regulator.

Ultimately I had to fix the generator.

There are two generators for 912 engines a 350W and starting in 1968, a 420W. Mine is the former, rated at 14V and 25 amps. They require different voltage regulators because the voltage regulator limits the amount of current from the generator. If you put the later voltage regulator on the earlier generator, it will regulate at 30 amps, and the life of the generator can be expected to be reduced. The rating is stamped on the body of my generator near the fan housing. It probably is on the later ones also.

My Problem

The generator light came on and would not go out independent of the engine rpm. The problems that could cause this include:
  1. V-belt not spinning the generator.
  2. Charging wire loose
  3. Charging wire defective
  4. Bad ignition switch.
  5. Bad regulator.
  6. Generator defective.

Visual inspection eliminated 1. and 2.

I decided that the after market regulator that came with the car when purchased was the most probable problem followed by a bad generator. Since the generator is expensive, a whole lot more work to replace and the regulator is relatively cheap; I decided to replace the regulator first. If this fixed the problem. I would not have do replace any expensive parts or do any analysis of more interesting possible problems.

A description of changing the generator is here.


112301-520 This image shows the diagram on the side of my new voltage regulator. There are 4 connections, B+ at the top and 3 more at the bottom. The Bosch part number on the box was 0 190 350 049.

Note:The B+ wire goes straight to the battery and is hot all the time! Be sure to disconnect the battery when working on the regulator.
112301-523 The connections on the bottom of the regulator from right to left are:
  • DF. - left most. This is a black wire from the DF (field) connection on the generator.
  • D-. - middle. This is the heavy yellow wire from case of the generator. It represents ground.
  • D+/61 - right most. The heavy red wire from the generator marked D+. This is the voltage output from the generator. In addition is a smaller blue wire that goes to the generator light on the dash. In the picture the blue wire comes in from the top right to the terminal.
112301-517 The final installation. This is nearly back to factory original. The mounting of the regulator is on the left wall of the engine compartment rather than on the sub-frame where the after market one had been installed. I had to get a new bolt and some elastic stop nuts at capture the regulator on its old rubber mounting points.
Last modified: Fri, 23 Nov 2001


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