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.

Broken Left Side Headlight Switch

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:

Parts List

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

New Switch Assembly with (8) Wires

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.

Wiring Circuit Board Inside Headlight Shell [Source: MAXBMW]

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.

Diode Symbol

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”

Wiring Circuit Board Areas Inside Headlight Shell [Source: MAXBMW]

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.

Old Switch Wires Removed and Grommet Removed

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.

Green/Black Wire Is A Ground Wire-Goes to Brown Section of Circuit Board

Then I install the two wires that go to the headlight relay, the Green/Purple and the Yellow/White

Green/Purple Wire Goes to Head Light Relay “86”

White/Yellow Wire Goes to Headlight Relay “87”

Next, I install the Green wire that goes to the ignition switch.

Green Wire Goes to Ignition Switch “56”

I finish up with the wires that go to the circuit board.

Yellow Wire Goes to Circuit Board Area “56b”

Brown/White Wire Goes to Circuit Board Area “H”

White Wire Goes to Circuit Board Area “56a”

Grey Wire Goes to Circuit Board Area “58”

2019-02-06 Added Electrical System Resources section. Allowed comments.

This content was originally published here.