Airhead Electrical Systems

I put together a series of pages about BMW airhead motorcycle electrical systems. It strikes me that electricity in general, and motorcycle electrics in particular, are dark mysteries to many, so I thought I’d shine some light [puns intended 🙂 ].

Lack of understanding hinders confidence when diagnosing and working on electrical projects. As these bikes age, the electrical system is prone to problems as corrosion and neglect makes them behave badly. More owners are having more electrical problems but seem less able to get to the root cause of the problem.

I think one tool that many avoid using is the wiring diagram. The spaghetti of lines, symbols and notations makes the eyes glaze over. “Oh goodness, where do I start?” is the common response to the advice, “Look at the wiring diagram.”

5 Series Wiring Diagram (1970-1973) (Source: Haynes Manual)

I’m not an electrical engineer, but I have taken time to learn the basics, have collected comments and input from well respected airhead mechanics and dug into how BMW applied electrical theory when they designed the /5 electrical system. I’ve learned a lot from various reference sources that are scattered about the internet, so my articles include a bibliography of various useful resources. That way both you and I have a nice set of reference materials to consult when problems come up.

Here are links to the documents which also appear on the index on the right side of the blog pages.

Due to the use of similar electrical components from the /6 series in the /7 series, I’m not adding a /7 series electrical components document. One significant change in the /7 series is the ignition system where BMW replaced the mechanical points system with an ignition control unit (ICU) with a Hall effect senor replacing the mechanical points.


2019-01-22  Add links to /6 Series documents.
2021-04-29  Add link to /7 Series, 1977 R100RS Circuits document.



6 thoughts on “Airhead Electrical Systems

  1. Brook,
    I thank you very sincerely for all the time and effort you put into this. I was fortunate to find a nice ’72 R60/5 Toaster in August 2017 and a ’73 R75/5 in December. As I type this I have my headlight bucket removed for paint on the ’73 and I really don’t think I would have moved forward with digging into the rats nest or wiring in that bucket if I hadn’t found your work here.

    At 61 years old I still have a couple of books and 3 ring binders with material my Dad collected (many pages are magazine articles) for reference on various technical/mechanical areas of interest for our old dirt bikes back in the late 60’s. I have printed this series of articles (along with blown up diagrams) from you and put them alongside my “library” inherited from my Pops … hopefully someday they will all sit on a shelf in my grown son’s shop! No doubt they will be plenty smudged from years of use … again, thank you Brook.

    • Hi Chris.

      Thank you for your note. I particularly liked the idea that some of my web documents ended up in hard-copy stored in a binder. When the internet melts down, my work will remain. 🙂


  2. Hi. Thanks for your efforts on this. I have an R80/7 that has gone completely dead, so I’m trying to immerse myself in the bmw electrical arts. Do you have any suggestions for /7 series component overviews/troubleshooting? Many thanks in advance

    • Hi David,

      If by “completely dead”, you mean can’t get a spark across the spark plugs, no lights and no starter, then logic leads toward the one component that powers everything. That’s the battery and it’s (+) cable. I would start proving the battery and (+) cable are functional. You should use a Volt/Ohm meter for the testing.

      If there is power in the Battery (+) equal to 12.6 volts, or pretty close, then wiring is the next to verify.

      The /7 electrical system is very similar to the /6 so you could use the /6 material I published to get you going. That said I would recommend you get a wiring diagram for your bike. They are available in the Haynes and Clymer manuals (and they do have some mistakes, but something is better than nothing). Euro MotoElectrics also provides diagrams.

      As to electrical diagnostics, start with a wiring diagram. You can start at the electrical component that’s not working. Prove there is, or is not power to the component. Work toward the battery continuing to prove there is, or is not power, in the wire and preceding component. When you find power, the next item upstream from that point that does not have power is likely the cause.

      I hope that helps.


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