The official BMW R90S Owners Club page

Headlight Circuit Description

Alan Menton

Here is a description of the headlight electrics I wrote for a friend some time ago. It might be of some use.

Here is a wiring diagram. It is useful because it has the numbers on wires/connections that are missing in the Clymer manual.

Power for the lights is fed by red wire 30. From the battery, it connect to 4 places. These have power all the time:

  1. clock
  2. headlight flasher
  3. ignition switch
  4. headlight relay


The flasher works when the ignition is off and by-passes the headlight relay. The flasher connects the live wire 30 to the white high beam light 56a.


When the ignition is on, power runs from the ig switch to the light on/off switch via green wire 56/31. When lights are switched on, 56/31 connects with 86. 86 takes the power that is delivered by 56/31 to the on/off switch up the the relay. When wire 86 is energised at the relay, a connection is made in the relay between the live red wire 30 and the yellow wire 87/56. Thus 56 becomes energised when 86 is energised, but 56 does not draw current from 86 but directly from the battery by connecting to red 30. 56 is the wire that takes the power to the Hi/LO beam switch. If Lo beam is sellected, 56 connects with yellow 56b. If Hi is selected, 56 connects with white 56a. Only other wire is in the relay is brown earth. And that's it.

To recap, the light On/Off switch is fed via 56 from the ignition switch. Only a small amount of current runs through the On/Off part of the handlebar switch. The handlebar on/off swithch turns the headlight relay on and off. When the relay is on, all of the current for the lights runs through the Hi/Lo switch.

Hope this helps.

Alan Menton
October 19, 2011

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