All German motorcycles are the same when it comes to wire work. People ask me all the time, “do you have a wire diagram”, for a certain motorcycle and I tell them yes I do but I always think to myself, it’s all the same. Basically the switch in the headlight has numbers on it. These numbers correspond to the respective places they go. For example the #58 is always the tail light on all motorcycles, including the BMW R12. The #30 is always the battery and so forth. Don’t ever be worried about a wire diagram and if it looks confusing, it’s not. So let’s start with the BMW R12. First is the electrical system.

You have two different types of electrical systems on the BMW R12. First is the BOSCH D2B magneto. This is the most common one you will find out there. This doesn’t require any power to start the motorcycle, it’s a magneto. When you kick the bike over and it spins it produces an electrical current to the plugs and creates a spark.

Here is the BOSCH D2B


The next Generator the R12 uses is the BOSCH 245RS108. This is for early BMW R12 motorcycles with dual carbs. You need power for this to work, it’s a battery generator.

Here is the BOSCH 245RS108

As you can see with the Image below both Generator and magneto are similar but different. On the Left is the BOSCH 245RS108 and on the right is the BOSCH D2B


This document below shows the correct Generator/magneto for the BMW R12 Single carb and dual carb motorcycle.


BMW R12 electrical wire diagram for a BOSCH D2B magneto

  1. Headlight
  2. Horn Button
  3. Horn
  4. Spark plugs
  5. Electrical connector for lights to the sidecar
  6. Rear tail light
  7. Sidecar Fender light
  8. Sidecar Rear fender light
  9. BOSCH D2B magneto
  10. Motor ground
  11. Battery

Here is the wire diagram for the BOSCH Generator 245RS108.

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