- Electrical System Resources
- Parts List
- Opening the Headlight Shell
- Inside the Headlight Shell
- Wiring Diagrams vs. The Circuit Board
- Left Control Switch Wires and Where They Go
- Remove the Old Wires and Switch
- Installing New Switch Wires Inside Headlight Shell
After I installed the wiring harness and headlight, the front forks and the handlebars, I replaced the left side handlebar control switch. This switch controls the headlights and horn. The headlight switch failed and my attempt to repair the switch was unsuccessful. So I have to replace it.
Electrical System Resources
I’ve been assembling information about the electrical system and have written several documents about it. You can find all my electrical system documents here:
Here the ones specific to the /6 series airheads.
I ordered the “long” version of the switch as I have “high bars”. There is another version available for the “short” or “Euro” bars such as used on the R90S bike.
|61 31 1 243 248||COMBINATION SWITCH LEFT – L=380MM|
Opening the Headlight Shell
I need to open up the headlight shell and fish out the old wires to remove the old switch and connect the new wires. This is easy to do by removing the screw at the bottom of the chrome headlight ring and rocking the ring upward. I put a towel on the front fender so the headlight can rest on it and not scratch the fender.
Inside the Headlight Shell
If you look inside a /6 series headlight shell, you can get overwhelmed by the nest of wires inside. Fortunately, with the introduction of the /6 series, BMW installed a “circuit board”. It is mounted in the middle of the shell. It is color coded to match wire colors and labeled to match the wiring diagrams, but only “sort of matching” as I’ll explain below. Also inside, on the right as you face the headlight, is the back side of the ignition switch and the headlight relay. On the left is the turn signal relay. The left handlebar switch has connections to the ignition switch and the headlight relay as well as the center circuit board.
Almost all the wires inside the headlight shell connect to the circuit board. This makes it a lot easier to find and replace wires than in the earlier /5 series headlight shell which didn’t have this board. Below is a picture of the board with the labels that are printed in each area highlighted around the perimeter.You will note that there are multiple terminals in each labeled-color coded area. All the terminals in that area connect together on the back side of the board. So, you don’t care which terminal a wire connects to in an area so long as the color code of the wire matches the color code of the area. So that makes things simple.
I have a Haynes manual that includes wiring diagrams and shows the wires in color to match the color codes. There are other sources for the wiring diagram, for example this one from Bob Fleischer on his site:
Wiring Diagrams vs. The Circuit Board
The problem I’ve found with the wiring diagrams when it comes to the circuit board is the diagrams don’t exactly match the labeled sections of the board. For example, most wiring diagrams show “15” on the diagram, but it really combines the wires that connect to “15u” and “15” at the top of the board. And, to confuse things a bit more, there is a second section of the board at the bottom left that is also labeled “15u”. When wiring diagrams show “15u”, they are referring to the one at the lower left of the board, NOT the one at the upper right. That’s why I said the wiring diagrams “sorta match” the circuit board.
The board sections are color coded to match the wire colors, so that’s very helpful. This greatly reduces the chance to incorrectly connect a wire to a terminal in the wrong section. For example, the “15u” section at the upper right of the board is colored Green, so only green wires connect to it while the “15u” section at the lower left is colored Green with Blue stripes, so only Green/Blue wires connect to it.
Wiring Diagram Area 15 and 15u Explained
If you look at the wiring diagrams carefully and check the wire colors that are shown connecting to area “15” of the circuit board you will notice that on one side of area “15”, all the wires are green and on the other side all the wires are Green/Black. You will also notice a symbol between the wires on the right side of the “15” section and the left side that is for a fuse. Now look at the picture above of the circuit board. Note that section “15” on the top left with the Green/Blue color code is on one end of the fuse and that section “15u” on the top right with the Green color code is on the other end of the fuse. Ah ha, so now you see what’s going on in the wiring diagrams. What the diagram labels as “15” really combines area “15”, the fuse, and area “15u” at the top of the circuit board. The other area “15u” at the bottom left of the circuit board is the section shown in the wiring diagram since it contains only the Green/Blue wires shown on the wiring diagram. This can really get you confused with two areas labeled the same, but each having different color code wires attached. No, I don’t know why BMW used the same label for two sets of different wires.
Wiring Diagram Area 58 Explained
The same approach is taken for area “58” on wiring diagrams: one side will show only Grey/Black wires which correspond to area “58” on the circuit board and the other side of the wiring diagram area “58” has only Grey wires connected which corresponds to area “58u” on the right side of the circuit board. Just like area “15” and “15u” above Area “58” and “58u” there is fuse in between and these two areas on the circuit board are connected to the fuse just Area “15” and “15u” are connected by their fuse. So, there is some logic to this after all.
Wiring Diagram Area 85b Explained
On the wiring diagrams area “85b” of the circuit board shows a symbol for a diode between the wires on the left side of the area and the wires on the right side.
On the circuit board, toward the bottom, is area “85b” color coded for Brown/Yellow wires and next to it at the edge of the board is area “LKK” that is color coded for Brown/Black wires. But, area “LKK” is not shown on all the wiring diagrams, only area “85b”. Well, you guessed it, on the wiring diagram, the wires that are Brown/Yellow connected on one side of area “85b” connect to area “85b” of the circuit board while the wires on the other side of “85b” in the wiring diagrams are Brown/Black so they connect to area “LKK” on circuit board. On the back of the circuit board between areas “85b” and “LKK” is the small diode shown on the wiring diagrams.
Should this diode fail, you get odd behavior of the starter. If this diode has shorted, when in gear and pulling the clutch lever, the neutral light will light up. If this diode is open (no circuit path through it), when in gear and the clutch lever pulled in, the starter motor will not work.
Left Control Switch Wires and Where They Go
The new left control switch has eight (8) wires. The list below shows the colors of the wires and where they go inside the headlight shell. Note, the ignition switch, headlight relay and turn signal relay are also inside the headlight shell along with the wiring circuit board. Some of the control switch wires go to the ignition switch and headlight relay. None of them go to the turn signal relay. Where you see “Area [some number]” it refers to labeled area of the circuit board shown in picture.
Wire Color Connects To
Green Ignition Switch “56”
Green/Black Area 31 “Ground”
Green/Purple Headlight Relay “86”
Grey Area “58”
Yellow Area “56b”
Yellow/White Headlight Relay “87”
White Area “56a”
Brown/White Area “H”
This handlebar switch has a ground wire that is Green/Black while the BMW standard is Brown for a ground wire. It’s the one case where a color code on a wire does not match the color code of the circuit board area it plugs into.
Remove the Old Wires and Switch
Before I start playing with the wires, I REMOVE THE BATTERY GROUND WIRE. I don’t want to loose any of the expensive and hard to find “BMW Smoke” that powers the electrical system 🙂
I use a pair of long nose needle nose pliers to pull and push the wires off the terminals. There is very little room for fingers next to the circuit board.
I remove the old wires and the large rubber grommet that seals them as they pass through a large hole on the top, left side of the headlight shell. As I remove the wires from the ignition switch and the headlight relay, I mark the color of the wire next to the terminal so it is easy to get the correct wire installed.
Installing New Switch Wires Inside Headlight Shell
The new switch includes a new rubber grommet for the headlight shell. I install the grommet and then push each wire through it one at a time. I start with the “funny ground wire”, the Green/Black wire, and plug it into the Brown color coded Area “31” toward the bottom of the board.
Then I install the two wires that go to the headlight relay, the Green/Purple and the Yellow/White
Next, I install the Green wire that goes to the ignition switch.
I finish up with the wires that go to the circuit board.
When I’m done, I connect the switch housing to the handlebar control. Then I connect the battery ground wire and test the switch to be sure all the functions work. The good news is none of the BMW smoke leaked out 🙂
2019-02-06 Added Electrical System Resources section. Allowed comments.
you have supplied lots of valuable information to many rebuilding these wonderful machines mine is a r90/6 1975
my question is where did you buy the switchgear from . I am in the uk and can only find used switches
I notice new ones are becoming scarce in the US as well. I did find a source for the left hand switch. It has extra long leads, but this excess can be coiled up inside the headlight bucket.
However, I haven’t found a source for a new right side switch. You might contact Tom Cutter in the USA at http://rubberchickenracinggarage.com/contact.html. He often has OEM parts that are no longer available.
I hope that helps.
Hello Brook, I have the HBSwitch732 from EME and it only has six wires. They are:
The switch does not have the toggle to turn the light completely off. My horn works and so does the flasher. However, I do not have high and low beam at all.
I believe the “731” switch has the added yellow lever that turns the headlight, parking light or off. The “732” does not have the yellow lever. The reason has to do with headlight function law in various countries. Some require the ability to turn off the headlight (USA) others did not.
Currently EME does not show the “732” in stock. I have noticed that MAX BMW is now showing both the “731” and “732” switches in their on-line parts fiche.
–> https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51649&rnd=07242017 (check under “61 Electrical”)
That said, showing them on their fiche does not guarantee MAX has any in stock, so I would call and verify before ordering a “731” if that’s the switch you need. I suspect EME might accept the “732” on return.
Thanks for your time Brook. The switch I really need for my 9/74 produced R90/6 is either 61 31 1 243 248 (380mm) or 247 (230 mm). I scoured for three years and came up empty. When I saw EME had their 732 available I went for it. My hope was to use it because the only difference was the yellow lever and I always ride with the light on anyhow. I guess my question is whether or not I can make it work for my application.
Well, I’ve not had to make that adaptation before.
When I look at the Haynes wiring diagrams for the 1975-76 bikes, and the 1983-84 bikes the “732” switch was made for, you need power to the headlight switch. On the original switch headlight power came from a RED wire that went inside the headlight shell and plugged into section (30) with the RED color code on the connector board. On the “732” switch, the GREEN wire is the power to the headlight. That goes to section (15U) on the left side of the top fuse. There ought to be an empty terminal in that section you can use.
The GREEN wires get power when the ignition is turned on. So the headlight goes out when you turn off the ignition. On the original switch, you could turn the headlight on with the ignition off since it got power directly from the battery via the RED wire.
I hope that helps.
Hi Brook, I took your advice and swapped the green wire to the 15U. Still no tail light or headlight (hi or low beam) although the flasher worked. I checked the 3-position ignition switch and found that in P, 30 and 58 had continuity. When turned On, 30, 15 and 56 had continuity but not 58. I plugged the yellow/white from the LH switch into 56 and all functions of the headlight worked but the tail light did not. I next took the grey off of terminal 58 and piggy-backed it with the yellow/white on 56 on the ignition switch. Everything worked. There are only three wires going to the light relay 1) a grey that goes from 86 to 58U on the board and then to the ignition switch, 2) a brown that goes from 85 to ground (31) on the board and a red that goes from 30 to 30 on the board on to 30 on the ignition switch.
You should consult a wiring diagram for your bike. It will help you understand what’s going on in your experiments. My quick guess is that your headlight relay is not working. Moving the YELLOW-White wire by-passed the headlight relay output to hi/low switch on the handlebar. That said, best of success in getting things wired correctly and working correctly.
This is great information! I replaced the left combination switch and I did connect everything as you did including the black/green to the brown.
Horn and high beam flash work but I don’t have low beam /high beam. Would you know what I could change to make it work?
There may be a relay issue?
my bike is 90/6 produced in January 1976
I recently completed a document about the wiring for this bike. There is information about how the high and low beam circuit works. Take a look and see if this helps you start looking for where the problem is.
/6 Series, 1975-76 Circuits
Headlight OFF-PARK-ON Switch & Relay Wiring
Headlight High/Low/Flash Switch-Low Beam
Headlight High/Low/Flash Switch-High Beam
Headlight High/Low/Flash Switch-High Beam Flasher
Using this information, you should be able to test the leads of the light relay to see if current flows into the relay, and depending on the combination switch position, if current is flowing out of the relay to the low beam and high beam filaments.
You will see that the high beam flasher circuit does not include the headlight relay, so the fact it is working suggests the relay, or the power wire to it, is the cause.
I hope this helps.
Great guide. Just followed it to change the left switch on my 75 90/6. However after double checking all, I still have no light in the headlight and rear light. Only break light and high beam blink. Everything else works like a charm. The old switch had nine wires, the new eight. A read one plugged into area 30 was left… any clue on where I have messed up? And thanks for all the stuff you have made available for hopeless amateurs like me. Have a great day.
You may want to look at this document I published on the /6 wiring circuits for the 1975-76 models.
–> /6 Series, 1975-76 Circuits
The newer version of the switch has 8 wires. It does not have the red wire that was used for the high beam flash when the ignition was off.
This style requires you to plug the green/black wire from the switch into the brown (ground) terminal section at the bottom of the terminal board inside the headlight shell. If you didn’t do that, there is no ground path for the headlight circuit. That would affect the headlight.
Another thing to check is if your connections to the headlight relay are in the correct locations, and the connections are tight.
And, check to see that the wires to the ignition switch are in the correct locations.
Assuming the ignition switch worked before you added the new left combination switch, it’s not likely it failed.
I hope this helps.
Thanks for you fast return. I would say I’ve done all of the above, but I’ll double check once daylight hits again. Just to make sure that all is in place properly.
Update from the eastern colonies:) seems like all wires a connected correctly and firmly. Only thing I could find, was that the black attached to the headlight was only hanging in a couple of copper strings – could this be the source of the evil that haunts the left switch?
When looking at various wire diagrams, it looks like there should be continuous power going into the switch (on the old switches via the red wire). Could I have gotten something odd, and get the power by splicing the old red to the white-yellow not the headlight relay? I’m looking for a straw. And during my time with the old lady, I’ve found a number of “interesting” solutions on electrics, nuts and bolts, and I fear that the previous owner has changed something inside the headlight bucket that he shouldn’t have..
And sorry if my English lacks a bit. Non native speaker.
I sent you a private email.
Hi , I need the LS headlight switch for my 1977 R100/7 . Or a repair kit because mine is pretty bad. If you have a new or used one or know where I would really appreciate it > Euro Moto -No ! , Motobins UK -No , etc etc .
I believe MAX BMW (https://shop.maxbmw.com/fiche/DiagramsMain.aspx?vid=51642&rnd=09082020) has one, part# 61 31 1 243 598. But it does not include the yellow headlight switch. You might call them and ask how to use it with your bike.