I’m going to replace the main wiring harness. This requires removing a number of connections inside the headlight shell, pulling the old harness out of the headlight shell and then installing the new harness and connecting the wires to the proper terminals on the wiring block, the headlight relay and the turn signal relay.  You do not have to remove the connections from the left and right handlebar switches to replace the main wiring harness.

NOTE:
Since I am converting the RS to an RT, that affects the handlebar switches as the cables need to be longer. However, someone replaced the left switch with the RT switch that has the longer 520 mm (about 20 inch) cable. The right switch got replaced with one that has a 380 mm (about 15 inch) cable instead of the stock RS switch with the 230 mm (about 9 inch) cable. But the right switch wires are still too short, so I have to add about 5-1/2 inches to the wires. I show how I do that in another document. 

Resources

Here is description of the standard wiring colors and terminal number used by BMW on wiring diagrams and electrical components. The colors and numbers are defined by the DIN standard used in Europe.

• Electrical Basics
  • Learning The Language of Wiring Diagrams

Here is a Haynes wiring diagram for the 1983-1984 RS & RT models (click to enlarge it).

NOTE:
Haynes diagrams do contain errors. This one mislabels a terminal on the headlight relay; it shows (87a) but it should be (87b). I believe the wiring for the connector board is correct and it’s easier to identify wire colors than the BMW issued diagram which maybe helpful to many inexperienced in converting German abbreviations for colors.

And, here is the BMW issued wiring diagram, courtesy of Tom Cutter at Rubber Chicken Racing Garage. I believe both diagrams are the same as regards the wires connected to the connector board, turn signal relay, headlight relay and both handlebar switches. And the BMW diagram also incorrectly identifies the headlight relay terminal (87b) as (87a). The DIN standard defines (87a) as normally closed and (87b) as normally open terminals. The headlight relay terminals are normally open, so (87b) is the correct designation.

NOTE:
When I refer to wire colors in this document, I use BOLD CAPITAL letters to indicate the solid color and Bold Initial Capital to indicate the stripe color. For example, a solid green with black stripe is noted as GREEN-Black.

Parts

Since BMW does not supply the main wiring harness any longer, I got one from Euro MotoElectrics:

•  Part# 61 11 1 244 098 –  WIRING HARNESS SECTOR CHASSIS (from 09/80)
  EME Part # Chassis-HAR098

Video

I made a video summarizing this work.

VIDEO: 1983 BMW R100RS Replace Main Wiring Harness

Main Wiring Harness Construction

Below is an overview of the various terminals and connectors on the main wiring harness starting from the ones that go inside the headlight shell.

Next in line near the steering head are the instrument cluster square plug and the fairing sub-harness plug.

Then, near the handlebars, come the clutch switch plug, the front brake light switch plug and then the white plug with the BLUE voltage regulator wire and the BLACK starter relay terminal (30) wire.

Next, near the voltage regulator and starter relay brackets, are the black starter relay socket and the white voltage regulator plug.

Near the coil brackets are the following set of wires:

• The BLACK coil Ignition Control Unit (ICU) trigger and tachometer wires terminal
• The GREEN–Blue coil power and ICU power wires terminal
• The GREEN–Red and GREEN-Black rear brake switch plug
• The BROWN frame ground wires ring terminal
• The BROWN–White horn wire terminals

At the end of the harness near the left battery side cover is the plug for the rear turn signal, brake and tail light sub-harness, and a plug with a BROWN-Black and a BROWN–Green wire that goes to the oil pressure and neutral switches.

Instrument Cluster Plug Pins

Here is the order of the pins on the instrument cluster plug.

Here is a map of what the instrument connector pins connect to inside the instrument cluster, and in parenthesis, the wire colors going into the pins.

• 1   – Nothing
• 2   – Neutral Ground (via switch) (BROWN-Black)
• 3   – Tachometer/Speedometer Bulb Power (GREY-Black)
• 4   – GEN Light Power (BLUE)
• 5   – Turn Signal Indicator, Right (BLUE-Black)
• 6   – Oil Pressure Ground (via switch) (BROWN–Green)
• 7   – High Beam Power (WHITE)
• 8   – Tachometer, Neutral, GEN, Oil Pressure Power (GREEN–Blue)
• 9   – Nothing
• 10 – Tachometer (BLACK)
• 11 – Turn Signal Indicator, Left (BLUE–Red)
• 12 – High Beam, Tachometer/Speedometer Bulb, Tachometer Ground (BROWN)

Main Wiring Harness Layout Inside The Headlight Shell

NOTE:
Traditionally, Left and Right are used from the perspective of where things are when you are riding the bike. To try to avoid confusion in the following sections, I use Left and Right from the perspective of what you are looking at. So, when looking into the headlight shell from the front of the shell, Left and Right are opposite to the traditional use of the terms when you are riding the bike. When I refer to the handlebar switches, I use the traditional meaning of Left and Right when describing the wires from these switches so the terms Left Switch and Right Switch will match what you see on a wiring diagram.

The main wiring harness enters the bottom of the headlight shell through a large grommet. The cable is secured with two metal clamps, one on the left bottom and the other at the center top, to the inside of the shell.

The wires in the main wiring harness bundle split into a left and right branch at the back of the headlight shell.

Connector Board

There is a connector board mounted to the back of the headlight shell. The wires in the left branch of the main wiring harness generally go to terminals on the left side of the board with the wires in the right branch generally go to the right side of the board.

The board is color coded into sections. The color code matches the colors of the wires that connect to that section. There is also a number, or letters, in each section. These correspond to terminal numbers the wire colors typically connect to. For example, the GREEN-Black section at the top left of the board has “15” inside it since GREEN-Black wires usually connect to terminal (15) on electrical components. The Resources section, above, has a complete description of the meaning of the wire color codes and the terminal numbers.

In the middle of the board are two terminals labeled “Reserve” in between the two mounting screws. On some year/models, these are spare terminals but on the 1983 RS/RT they are used.  The two 8 amp fuses go between terminals (15U) and (15) and between (58U) and (58). Power comes in on 15U and 58U and if the fuses blow, no current flows to the terminals in (15) or (58).

NOTE:
There are two sections labeled (15U), the upper right with GREEN wires and lower left with GREEN–Blue wires. The lower left section is not used. The two GREEN–Blue wires are connected together but not on the connector board.

On the back of the connector board, are electrical buses that connect all the terminals in a section so they act as a single electrical connection. Therefore, you can connect wires to any terminal in a section to make the connection (see picture below).

There are two special sets of terminals near the bottom left hand side; (LKK) and (85b) that are next to each other. On the back of the board is a diode connected between the buses of these two terminal sections. A diode allows current to flow only in one direction. The diode is installed so that current can only flow from section(85b) to section (LKK) unless the diode fails. I tested the diode with a volt/ohm meter and I had zero resistance in one direction and an open circuit in the opposite direction, so the diode is working correctly.

NOTE:
The diode can fail in two ways, it can short out allowing current to backflow form the (LKK) terminals to the (85b) terminals, or it can open preventing current flow between the terminals on (85b) to the terminals on (LKK).

Symptoms of a shorted diode is when pulling the clutch lever towards the handlebars, the neutral lamp is lit. Symptoms of an open diode is that the starter motor will not work when the transmission is in neutral, but it will work when you pull the clutch lever.

Wires That Connect But Not On The Connector Board

There are a couple wires that connect to each other, but don’t use terminals on the connector board.

A GREEN wire that goes to the ignition switch has a male spade terminal that plugs into a wire with a female spade terminal. I disconnect them.

There is a GREEN–Blue wire with a male spade terminal that connects to a GREEN–Blue wire with a female spade terminal. I disconnect them.

Turn Signal Relay

The turn signal relay mounts on the left side of the headlight shell.

The green relay plugs into a socket. I unplug the relay so I can get access to the screw that secures the socket to a bracket on the side of the headlight shell. I remove the relay socket so it is easier to access the wires plugged into the connector block.

Headlight Relay

The headlight relay mounts on the right side of the shell. It is secured with a chrome plated Allan screw that goes through a hole in the headlight shell. I remove the relay so it is easier to get to the wires on the connector block.

The original headlight relay is special. It has a diode between terminals (86) and (87)-(87b). The diode prevents back current through the headlight relay. If current can flow the wrong way, it leads to the bike still running even when you turn the ignition switch off. This relay is the correct relay, BOSCH SR 9736, BOSCH Part# 1243051.

Handlebar Switches and Ignition Switch Wire Bundles

The handlebar switch wire bundles enter the headlight shell through holes on the top of the shell on the left and right. The ignition switch wire bundle enters the headlight shell through a smaller hole just under the right handlebar switch wire bundle.

NOTE:
When looking at the inside of the headlight shell from the front, the right handlebar switch is on the left side of the headlight shell.

Remove Main Wiring Harness Wires

I start by pushing the ignition wiring bundle back inside the headlight shell. I use a small Phillips head screw driver to force the grommet inside the headlight shell. Then I push one connector at a time inside the headlight shell along with it’s wire.

What Wire Goes Where?

I made a spreadsheet diagram that represents the terminals on the connector board as shown below. The black bar with “Reserve” inside it represents the center of the connector board. I did not show the fuses between sections 15U and 15,  and between 58U and 58 in the diagram.

The terminals in each color coded section of the board are within a box and are numbered “1-“, “2-” etc. The color code and terminal number of the section is next to the box. I use two-letter codes, shown in the table under the diagram, to identify all the sources of wires inside the headlight shell.  I enter the source code next to the terminal number. If there is more than one wire on the connector, I note how many with “-x” after the source code where “x” is the number of wires. If just the terminal number is shown, e.g. “1-“, there is no wire on that connector board terminal. Obviously, the wire color is the same as the color for that section of the connector board.

NOTE:
On this year/model, the Reserve terminals in the center are used to connect ignition switch GREEN–White wires together. On other year/models, these terminals can be empty.

After I made the entries in the spreadsheet, I remove the main wiring harness wires on the left side of the connector board first followed by wires on the right side. As I go, I verify the wires I remove against the spreadsheet. I find a couple mistakes and correct the spreadsheet: Checking the wires twice is a good idea to prevent mistakes.

I start by disconnecting the two GREEN and two GREEN–Blue wires that are connected off the connector block.

Then I remove the wires on left side of the connector block, followed by the wires on the right side.

Remove Wires From Turn Signal Relay Socket

The turn signal relay socket has two wires that are secured into the bottom of the socket. One is BROWN ground wire from the right branch of the main harness and the other is a GREEN-Black wire from the left branch. I need to remove them from the socket.

Before I remove the wires I put some masking tape on the side of the turn signal relay socket showing which side has the BROWN and GREEN-Black wires to make it easy to install the new wires in the correct hole of the socket.

I use a small thin blade screw driver to release the female spade terminal from the socket. Looking at the socket from the top, there is a notch on the edge of the hole for the terminal that is next to the side of the socket. I insert the screw driver  into the hole, wiggle it a couple times and then I can pull the female spade terminal out of the socket. It is secured by a small tab which I flatten when I insert the screw driver.

The bottom of the relay has terminal numbers, so if you don’t put tape on the socket to help you get the wires back into the correct hole, you can figure out which side has the BROWN wire as BROWN wires always go on terminal (31). Since the relay only goes one way in the socket, you can use it identify which hole gets the BROWN ground wire.

NOTE:
The GREEN-Black wire usually goes on terminal (15), but this is a case where it does not as it goes on terminal (49) of the turn signal relay.

Disconnect Headlight Relay Wires

All the main wiring harness wires that go to the headlight relay are in the right side bundle of wires. Even though the terminals on the bottom of the relay are numbered, I made a diagram of what wires go to which terminal as I remove them. There is a mounting tab on the relay and I oriented it at the bottom as I remove the wires, so that’s the orientation of the diagram below. The YELLOW–White wire does not have to be removed as comes from the left side handlebar switch.

Identifying Main Harness Wires In Left and Right Branches

As shown earlier, the wires of the main harness split to the left and right sides of the connector board. Wires with the color codes that match the sections on the left are in the left branch. I made a table of the wires I found in the left and right branches when I removed the wire wrapping from each bundle.

Remove Main Harness From The Shell

Now that I have all the wires disconnected, I use a screw driver to push the large grommet out of the shell. Then I push the wires out of the shell one terminal at a time until they are all removed.

Install New Main Wiring Harness

Assembly is not the reverse of disassembly, it’s in the same order. Here is the new harness and the wires that go into the headlight shell.

Protection From Corrosion

I put some NO-OX-ID “A-Special” I got from Euro MotoElectrics on the terminals. This is a conductive, anti-corrosion paste that should help keep the connections from tarnishing and corroding. I think this is a better solution for prevention of corrosion on wiring terminals than dielectric grease which is non-conductive.

Insert Ignition Switch Wires

I start by pushing the ignition switch wires into the headlight shell through the hole in the bottom of the shell since they are the  longest. Then I push the four wires (RED, GREY, GREEN, GREEN-White) that go to the ignition switch through the hole in the back of the headlight shell under the right handlebar switch wires. When I get them through, I use a screw driver to seat the grommet by pushing it to the outside of the headlight shell.

There are some ignition wires that remain inside the headlight shell: a GREEN-White, a GREY wire that has two wires connected to the spade terminal, and a GREEN wire that has a male spade terminal.

There is a large rubber grommet on the end of the main wiring harness that seals it in the hole at the bottom of the headlight shell. I push it down the sheath since about eight inches or so of the sheath goes inside the shell. Next I push the rest of the wires inside the headlight shell starting with the longest ones first.

Group Wires Into Left and Right Branches

Using the list of wires that go into each branch inside the headlight shell that I created when I removed the wires, I group the wires into the left and right branches and secure the bundles with some velcro wire organizer ties.

Install Wires On Connector Board

I start with the left side of the board. I use the map I made of where the main wiring harness wires connect to the terminals on the connector board. I start at bottom of the left side of the board and work my way up. Then I install the wires on the right side of the connector board. It takes some attention to detail as I found it would be neater if I removed a wire and rearranged it to reduce the tension on it or I could reduce the “rat’s nest” appearance of  the wiring.

Install GREEN-White & Off-board Wires

I install the GREEN-White wire from the ignition switch on a Reserved terminal in the center of the connector board.I connect the other GREEN-White wire that goes from the headlight switch to the Reserved terminal as shown below.

I connect the two GREEN wires and the two GREEN–Blue wires that connect off the connector board. In each pair one has a male and the other a female spade terminal.

Install Spade Connectors In The Turn Signal Relay Socket

There is a BROWN ground wire lead from the ground wire connected to section (31) of the connector board that plugs into the turn signal relay socket and a GREEN-Black wire lead from the 3-wire GREEN-Black wire connected to section (15) of the connector board that plugs in across from the BROWN wire. I just insert the female spade terminals into the correct slot of the plug with the tab side of the terminal pointing to the outside edge of the socket and the tabs on the terminals lock them into place.

Then I mount the turn signal relay socket on the tab on the left side of the headlight shell with the mounting screw, put NO-OX-ID on the relay terminals and plug it into the socket.

Install Wires On Headlight Relay

I made a wiring diagram of the wiring of the headlight relay when I removed the main wiring harness. I plug the new wires in accordingly. Then I mount the relay on the right side of the headlight shell using the Phillips screw, wave washer and nut.

What All Done Looks Like

The inside of the headlight shell is still full of wires, but I think they are laid out in a way that minimizes the “rats nest”.

Revisions

2020-04-02  Updated wiring diagram text, added BMW diagram.
2020-04-03  Add details to headlight relay.
2020-07-28  Update connector board diode with test result.