I am converting this 1983 R100RS into an RT configuration. Since the RT handlebars are much longer than the RS bars, the stock RS handlebar switch wires are too short; 230 mm (9 inches) vs.the RT switch’s 520 mm (20 inches). However, someone replaced the left handlebar switch with an RT length switch, so that’s fortunate. The right handlebar switch also was replaced but with shorter 380 mm (about 15 inches) wires. So the right side switch wires are too short.

Handlebar switches for the 1983 models are unavailable. So I’m going to lengthen the wires of the right side switch by adding 140 mm (5.5 inches). But, unlike barbed wire, I can’t use my wire stretcher, so I have to splice some wire into each of the right side handlebar switch wires. 🙂

I’m also going to replace the headlight shell grommet for the left switch as it’s shot.

Materials

• Stranded 16 gauge wire,

• Electrical wire solder,

• Motion Pro “Nitro Tape”,

• “Liquid Tape”.

• Rubber Grommets from Harbor Freight’s kit.

Tools

• Wire strippers with dies that fit multiple gauge wires for a clean strip.

• 200/260 watt soldering gun

Resources

Here is description of the standard wiring colors and terminal numbers 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 wiring diagram for the 1983-1984 RS & RT models (click to enlarge it).

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.

Video

Here is a short video summarizing this work.

VIDEO: 1983 BMW R100RS Lengthen Handlebar Switch Wires

Remove Switch Wires From Headlight Shell

It’s much easier to do this work with the right handlebar switch on my work bench. So I remove the switch wires from inside of the headlight shell making note of what wire goes where.

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 divided into color coded sections. The color code matches the colors of the wires that connect to terminals in 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.

What Wires Go Where

Previously, I replaced the main wiring harness and I made a spreadsheet that maps where all the wires attached to the connector board go. I use that to help me find the right handlebar switch wires (RS) and to install them again on the correct terminal.

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.

Based on the diagram above, I remove the “RS” wires from the connector board. But, the right side switch also has two connections that go to wires not attached to the connector board. Here is a list of the wires from the right handlebar switch and where they connect inside the headlight shell.

• GREEN: Connector Board Section (15U); has two wires on one terminal.
  This wire has a lead that connects to a wire from the ignition switch. Those two wires are NOT attached to the connector board. I separate the connection to release the right switch GREEN wire.

• GREEN–Blue: This wire is not attached to the connector board. It connects to another GREEN–Blue wire off the board. I separate the connection so I can remove the right switch GREEN–Blue wire.

• BLUE–Yellow: Connector Board Section (85)
• BROWN–Yellow: Connector Board Section (85b)

Here is where the BLUE–Yellow and BROWN–Yellow wires are located on the connector board.

I pull all the right side switch wires out of the headlight shell along with the grommet.

Preparing The Splice

I use a sharp knife to cut through the black outer sheath bring careful not to cut the insulation on the wires inside. Then I pull the sheath down the wire several inches to expose the wires inside.

Then I cut the wires on a staggered offset. I want the solder joints to be distributed and not all bunched together. This protects against short circuits should the solder joints chaff through the shrink tube insulation I will install. And, it avoids having a fat spot in the harness created when all the splices are on top of each other.

Making the Splice

I cut four pieces of 16 gauge stranded wire each the same length; 5-1/2 inches. I strip about 1/4 inch of insulation off the ends and off the ends of the cut switch wires. I untwist the wires and straighten them.

I put two pieces of large diameter shrink tube on the switch end of the switch cable. I use these to cover the splices on both ends of the cable after install the four splice wires.

I put the new grommet over the end with the wires that go inside the headlight shell. It’s easier to slip the grommet over the cut ends of the wire than threading the terminals through the grommet after the splices are completed.

I put smaller shrink tube on one of the splice wires and butt splice one end of the wire to the shortest wire of the switch cable on the end with the switch. A butt splice is where straight strands of two wires are pushed together so they slide past each other. This keeps the diameter of the soldered splice small so there isn’t much of a bulge.

I solder the joint, let it cool, slide the small shrink tube over the splice, and heat it to shrink it over the solder joint. This insulates the solder joint.

Before I butt splice the other end of the splice wire to the matching color wire on the terminal end of the cable, I put another small piece of shrink tube on the splice wire, and I make sure the other end of the splice wire goes on the same color wire as the already soldered end. Then I butt splice it, solder it and shrink the shrink tube over the solder joint.

NOTE:
Since I staggered the cuts of the wires inside the cable, and I started splicing on the shortest wire on the switch side, the other end of the splice wire goes on the longest wire on the terminal end. This pattern is helpful in being doubly sure I always put the ends of the splice wire between the ends of the same color wire in the cable . Of course, I verify the colors are the same, but I like to have a “belt and suspenders” approach when doing wiring work.

I continue this way with the other three splices until all four wires have been spliced. I verify once more that each splice wire has the same color cable wire on both ends.

Finishing Up

I insert the terminals back inside the headlight shell, connected them where they belong, and seat the new grommet in the headlight shell hole. Then I slide the large shrink tube over the splices on each end of the cable overlapping them a bit on the ends of old sheath and shrink it to help keep water out of the solder joints.

I wrap Nitro Tape over the larger diameter shrink tubing starting it on the outer sheath about an inch past the end of the shrink tube. This will keep water from getting into the spliced wires and the solder joints and keeps the spliced wires bundled together like the original sheathing did.

Replace Left Switch Harness Grommet

Okay, I did this the quick and easy way. I cut the old grommet and removed it. Then I sliced through the side of the new grommet and installed it into the headlight shell. To keep the new grommet from leaking, I applied “Liquid Tape” over the cut edge of the grommet inside and outside the headlight.

There are eight wires in the left switch cable so it’s very tight to try and push all the terminals through the grommet. And, the grommets are hidden inside the fairing, so the dab of Liquid Tape isn’t visible.

Both switch cables are now the same 520 mm (20 inch) length needed to fit the RT handlebars.