61 BMW 1983 R100RS/RT Install Electrical System

I’m converting this bike from and RS to a RT model, so there are some changes associated with the RT model, but the electrical system changes are limited to changes in cable lengths for the handlebar switches.

This document references other documents previously published as well as containing new material. The idea is to consolidate information about how I install the electrical system on the bike in one place.

Main Harness & Handlebar Switch Wiring

I show how I install the main wiring harness in the headlight shell, route it, lengthen a handlebar switch cable and install the handlebar switches in the perches in these documents.

Charging System & Ignition System

I show how I install the engine electrical components that make up the charging system and ignition system here.

Starter Relay

I replace the main wiring harness which includes a new starter relay plug. The relay plug mounts to a bracket on the left side of the frame spine tube. I mount it to the rear set of threaded screw holes in the bracket.

Starter Relay Bracket Location

Starter Relay Bracket Location

There is a red wire from the battery (+) terminal that brings power to the starter relay, and in fact, to all the other components on the bike. It needs to be installed into the starter relay plug. I show where and how to install that here:

Voltage Regulator

I show how I  install the voltage regulator here:

Fairing Sub-Harness

The fairing sub-harness plugs into a socket on the main wiring harness. It connects to the two front turn signals and parking light, the volt meter and the clock. Both the clock and volt meter have bulbs for illumination when the parking light or headlight are on and the clock gets power (RED) from the battery even when the ignition is off so the clock runs all the time.

NOTE:
The parking lights are on if the parking or headlights are selected.

Fairing Sub-Harness

Fairing Sub-Harness

Fairing Sub-Harness Plugs Into Socket On Main Wiring Harness

Fairing Sub-Harness Plugs Into Socket On Main Wiring Harness

Here is a table of wire color to component and pictures of which wires go where in the sub-harness plug. The plug is designed to go only one way into the main harness socket so you can’t install it backwards.

Wire Color                     Component                                                                 
BROWN                          Ground
BLUERed                      Left Turn Signal Power
BLUE-Black                   Right Turn Signal Power
GREY-Black                   Parking Light, Clock & Volt Meter Illumination Power
GREEN-Black                Volt Meter Power
RED                                Clock Power

Fairing Sub-Harness Plug Wires

Fairing Sub-Harness Plug Wires

Fairing Sub-Harness Plug Wires

Fairing Sub-Harness Plug Wires

I show how the wires connect to the turn signals, parking light, volt meter and clock with these out of the fairing so it’s easier to see where the wires connect.

Right Front Turn Signal Wires Detail

Right Front Turn Signal Wires Detail

Front Parking Light Wires Detail

Front Parking Light Wires Detail

Clock Wires Detail

Clock Wires Detail

Volt Meter Wires Detail

Volt Meter Wires Detail

Left Front Turn Signal Wires Detail

Left Front Turn Signal Wires Detail

I show how I install the turn signals, front parking light, volt meter and clock in the document showing how I install the fairing.

Ignition Switch

The ignition switch has four wires that attach to numbered terminals on the bottom of the switch as shown in the table below:

Ignition Switch Terminal Numbers

Ignition Switch Terminal Numbers

Wire Color                     Terminal (#) – Component                                    
RED                                (30) – Power From Battery
GREEN                           (15) – Power To Top Fuse In Headlight Shell
GREY                           
 (58) – Power To Bottom Fuse In Headlight Shell
GREENWhite                (56) – Power To Headlight Relay

There are two terminal (30) connections on the back of the switch but I only need to use one of them.

I attach the wires to the appropriate terminal. I show how to install the switch in the dash board in the document about installing the fairing.

Ignition Switch Terminals

Ignition Switch Terminals

RED-Terminal (30)

RED: Terminal (30)

GREEN-Terminal (15)

GREEN: Terminal (15)

GREY-Terminal (58)

GREY: Terminal (58)

GREEN-White: Terminal (56)

GREEN-White: Terminal (56)

Horns

The horns mount to brackets on each side of the frame. They mount to metal straps that are designed to amplify the horn vibration to increase the volume. I cleaned the horns and straps before mounting them.

Horn Strap Mounting Hardware

Horn Strap Mounting Hardware

The bolts have flat washers on the outside of the strap and a serrated washer on the inside of the strap. They are secured to the tab on the frame with a nut and lock washer.

Horn Strap Hardware Detail

Horn Strap Hardware Detail

Horn Strap Hardware Detail

Horn Strap Hardware Detail

Horn Strap Hardware Detail

Horn Strap Hardware Detail

I rotate the horns so the mouth points towards the front and the ground to keep water from accumulating inside the horn mouth. I put the plastic vanity cover on the strap bolt head and attach the BROWN-White wire to the horn terminal. The ground path is via the strap mounting bolt.

Bolt Head Vanity Cover

Bolt Head Vanity Cover

Vanity Cover Attached To Bolt Head

Vanity Cover Attached To Bolt Head

Attach Left Side Horn BROWN-Whits Wire To Horn Terminal

Attach Left Side Horn BROWNWhite Wire To Horn Terminal

Battery Box & Battery

The battery box is secured with four rubber isolation damper mounts; two on the bottom and two on the top.

NOTE:
On earlier airheads, five isolation dampers were used; three on the bottom and two on the top. And, later versions of the isolation damper have one stud that is longer than the other. If you use them for the bottom of the battery bracket, BE SURE the short stud is underneath the battery as the longer stud can abrade the battery case.

On this bike, the isolation damper on the top, right side of the battery bracket has a longer stud on one side. The  long stud points to the rear and the rear brake reservoir mounts on that stud. Each stud on the isolation damper is secured with a nut and wave washer.

Battery Box Vibration Isolator Studs-Lower Right Isolator With Longer Stud On One Side Is Used On Top Right Of Battery Box

Battery Box Vibration Isolator Studs-Lower Right Isolator With Longer Stud On One Side Is Used On Top Right Of Battery Box

Battery Box Vibration Isolator Hardware

Battery Box Vibration Isolator Hardware

Two isolation dampers go on the outside holes at the bottom of the battery box and are secured to the frame bracket with nuts and wave washers underneath the bracket. The battery box is secured to the other stud of the isolation damper with another nut and wave washer. The top frame brackets get isolation dampers, and the right top bracket gets the damper with the long stud pointing to the rear.

Two Bottom Vibration Isolators Mounted To Frame Bracket

Two Bottom Vibration Isolators Mounted To Frame Bracket

Top Left Vibration Isolator Is Same As Bottom Isolators

Top Left Vibration Isolator Is Same As Bottom Isolators

Top Right Vibration Isolator Has Long Stud Pointing To Rear

Top Right Vibration Isolator Has Long Stud Pointing To Rear

The battery box is ready to hold the battery.

Battery Box Mounted-Note Only Two Vibration Isolators Are Used On The Bottom

Battery Box Mounted-Note Only Two Vibration Isolators Are Used On The Bottom

Battery Box Mounted And Ready For The Battery

Battery Box Mounted And Ready For The Battery

I slide the battery into the battery box between the sub-frame rails from the top. Then I attach the retaining bracket with the channel facing up and tighten the two plastic nuts on the battery box posts.

Battery Drops Into Battery Box From Top

Battery Drops Into Battery Box From Top

I attach the RED battery (+) cable that goes to the starter motor to the left terminal along with the auxiliary socket (+) wire.

Battery (+) Terminal With Starter Motor and Auxiliary Socket Wires Attached

Battery (+) Terminal With Starter Motor and Auxiliary Socket Wires Attached

I attach the BLACK ground wire to the battery (-) and route it so it won’t put strain on  the speedometer cable bolt. I also attach the auxiliary socket ground wire to the battery (-) terminal.

Battery (-) Terminal With Ground Cable and Auxiliary Socket Ground Wire Attached

Battery (-) Terminal With Ground Cable and Auxiliary Socket Ground Wire Attached

Battery (-) Cable Routing To Avoid Strain On Speedometer Bolt

Battery (-) Cable Routing To Avoid Strain On Speedometer Bolt

Battery (-) Cable Routed To Speedometer Cable Breather Bolt To Avoid Strain On The Bolt

Battery (-) Cable Routed To Speedometer Cable Breather Bolt To Avoid Strain On The Bolt

Rear Brake Light Switch & Sub-Harness

I replaced the rear brake light switch. It mounts on a bracket inside the right arm of the muffler & rear foot peg bracket. Two screws secure it in tapped holes in the bracket.

Rear Brake Light Switch Bracket Inside Right Side Muffler and Foot Peg Bracket

Rear Brake Light Switch Bracket Inside Right Side Muffler and Foot Peg Bracket

New Rear Brake Light Switch Parts From EME

New Rear Brake Light Switch Parts From EME

I mount the switch on the bracket with the two Phillips screws and lock washers. The screw closest to the inside of the muffler bracket is accessed from the hole in the top of the muffler bracket. The plunger of the switch points to the front of the bike.

Attach Rear Brake Light Switch Screw Closest To Bracket Using Access Hole

Attach Rear Brake Light Switch Screw Closest To Bracket Using Access Hole

Plunger Of Rear Brake Light Switch That Rear Foot Pedal Pushes

Plunger Of Rear Brake Light Switch That Rear Foot Pedal Pushes

The rear brake light switch attaches to a sub-harness. I route the sub-harness through the hole of the gusset on the rear of the frame. The plug on the other end of the sub-harness plugs into a socket on the main wiring harness under the rear of the frame spine tube.

Rear Brake Light Switch Sub-Harness From EME

Rear Brake Light Switch Sub-Harness From EME

Rear Brake Light Switch Sub-Harness Routed Via Hole In Rear Frame Gusset

Rear Brake Light Switch Sub-Harness Routed Via Hole In Rear Frame Gusset

Rear Brake Light Sub-Harness Plug Connects To Socket At Rear Of Main Wiring Harness

Rear Brake Light Sub-Harness Plug Connects To Socket At Rear Of Main Wiring Harness

The rubber cover has scores for the wires and I push them through the cover. The wires exit the cover facing the outside of the bracket so they are protected. The wires attach to the two screw pinch terminals on the rear brake light switch.

Wires Pushed Through Scores In Rubber Cover

Wires Pushed Through Scores In Rubber Cover

Wires Pushed Through Scores In Cover

Wires Pushed Through Scores In Cover

Rear Brake Light Switch Pinch Screw Terminals

Rear Brake Light Switch Pinch Screw Terminals

Attach Wires To Switch Terminals With Pinch Screws

Attach Wires To Switch Terminals With Pinch Screws

I mount the cover so the wires exit next to the inside of the muffler bracket and I route the sub-harness cable along the rear frame tube in front of the rear battery bracket so the cable is out of the way and connect it to the main wiring harness socket.

Route Brake Light Switch Wires Next To Muffler Bracket

Route Brake Light Switch Wires Next To Muffler Bracket

Rear Brake Light Switch Sub-Harness Routed In Front Of Rear Battery Bracket

Rear Brake Light Switch Sub-Harness Routed In Front Of Rear Battery Bracket

Auxiliary Power Outlet & Sub-Harness

This bike has the optional auxiliary power socket with a fuse holder for a 8 amp fuse the same as the two that fit on the connector board inside the headlight shell. The cable has cracks in the outer insulating sleeves and the rubber grommet that fit over the terminals on the back of the socket is cracked and not water tight.

Original Auxiliary Socket Sub-Harness Connects Directly To Battery

Original Auxiliary Socket Sub-Harness Connects Directly To Battery

Original Water Proof Grommet For Socket Terminals Is Shot

Original Water Proof Grommet For Socket Terminals Is Shot

Original Water Proof Grommet For Socket Terminals Is Shot

Original Water Proof Grommet For Socket Terminals Is Shot

The bracket was rusting in places and I repainted it.

Auxiliary Socket Bracket Mounts to Left Upper Shock Bolt And Is Rusty

Auxiliary Socket Bracket Mounts to Left Upper Shock Bolt And Is Rusty

Auxiliary Socket Sub-harness Bracket Removed Before Clean Up And Paint

Auxiliary Socket Sub-harness Bracket Removed Before Clean Up And Paint

Repainted Auxiliary Socket Bracket With Socket Installed

Repainted Auxiliary Socket Bracket With Socket Installed

Before I repaired the grommet on the harness, I marked the end of the wire that plugs onto the center terminal of the socket with red paint as that’s the terminal that connects to the battery (+) cable. I also painted a red band on the other end of the cable. I used my volt/ohm meter to verify the wire ends were on the same wire.

I Put Red Paint On Terminal That Goes On Center Pin Of Plug

I Put Red Paint On Terminal That Goes On Center Pin Of Plug

I Put Red Paint On Battery (+) Ring Terminal That Mounts On Battery

I Put Red Paint On Battery (+) Ring Terminal That Mounts On Battery

Installation of the bracket and socket is straight forward. The socket attaches to the bracket with a large nut and the bracket fits on the shock bolt secured by the shock top mounting nut.

Auxiliary Bracket Mounts To Top Left Shock Bolt

Auxiliary Bracket Mounts To Top Left Shock Bolt

Auxiliary Socket Bracket Installed

Auxiliary Socket Bracket Installed

I repaired the sub-harness using some shrink wrap over the cracks in the outer insulation. But the grommet over the socket terminals is a 90 degree cover. I oriented the socket in the bracket so ground terminal is at the top. I used three pieces of large diameter shrink wrap to cover fabricate a cover. After heating the shrink wrap tubing I used “Liquid Tape” and painted over the shrink warp to create a water tight seal over the exposed socket terminals. It’s not pretty but it is water proof.

Socket Installed Showing Terminal Orientation

Socket Installed Showing Terminal Orientation

Fabricating 90 Degree Water Proof Cover From Three Pieces Of Large Diameter Shrink Tubing

Fabricating 90 Degree Water Proof Cover From Three Pieces Of Large Diameter Shrink Tubing

Liquid Tape

Liquid Tape

Final Grommet Repair-Not Pretty, But Water Proof

Final Grommet Repair-Not Pretty, But Water Proof

I oriented the water proof cover on the front of the socket so it goes up when open to keep water from entering around the seal.

Rubber Water Proof Cover On Front Of Socket Hings Up

Rubber Water Proof Cover On Front Of Socket Hings Up

Orientation Of Rubber Water Proof Cover On Front Of Socket

Orientation Of Rubber Water Proof Cover On Front Of Socket

Tail Light, Brake Light & Rear Turn Signals & Sub-Harness

The tail light, brake light and rear turn signals are connected on a sub-harness that plugs into a socket at the rear of the main wiring harness.

Rear Sub-Harness Connects To Tail Light Assembly

Rear Sub-Harness Connects To Tail Light Assembly

Rear Sub-Harness (Right) Plugs Into Socket On End Of Main Wiring Harness

Rear Sub-Harness (Right) Plugs Into Socket On End Of Main Wiring Harness

Here is a table of wire color to component and pictures of which wires go where in the sub-harness plug. The plug is designed to go only one way into the main harness socket so you can’t install it backwards.

Wire Color                     Component                                                                 
BROWN                          Ground
GREENRED                  Brake Light Power
BLUERed                      Left Turn Signal Power
BLUE-Black                   Right Turn Signal Power
GREY-Black                   Parking Light Power

Rear Sub-Harness Plug Wires

Rear Sub-Harness Plug Wires

Rear Sub-Harness Plug Wires

Rear Sub-Harness Plug Wires

The tail light housing includes terminals for the turn signal wires that go down the stems to the turn signal reflectors.

Left Rear Turn Signal Wire Connections On Back Of Reflector

Left Rear Turn Signal Wire Connections On Back Of Reflector

Right Rear Turn Signal Wire Connections On Back Of Reflector

Right Rear Turn Signal Wire Connections On Back Of Reflector

The tail light housing has terminals for attaching the wires the go to the turn signals. These wires are threaded down the turn signal stalk the signals attach to.

Tail Light Housing Parts

Tail Light Housing Parts

Tail Light Reflector Wiring With Bottom Of Reflector At Top: <strong><span style="color: #999999;">GREY</span>-Black</strong> is Parking, <strong><span style="color: #00ff00;">GREEN</span>-<span style="color: #ff0000;">Red</span></strong> Is Stop Light, <span style="color: #800000;"><strong>BROWN</strong> </span>is Ground

Tail Light Reflector With Bottom Of Reflector At Top: GREY-Black is Parking, GREENRed Is Stop Light, BROWN is Ground

The tail light reflector has two single filament bulbs; the top is the brake light and the bottom is the tail light. The top bulb is 21 watts while the tail light is 5 watts which is marked on the reflector.

Rear Reflector: (Top) Brake Light; (Bottom) Tail Light

Rear Reflector: (Top) Brake Light; (Bottom) Tail Light

Brake Light - 21W

Brake Light – 21W

Tail Light - 5W

Tail Light – 5W

Testing Electrical System

After I hooked up the battery, I tested the electrical system. I turned the ignition switch OFF, then to PARK and then to ON. Here’s what did work, didn’t work and what I found out the cause is.

-Oil PressureOKLights When Turn Signal Switch On

Ignition Switch On OFF
Component                   Status  Note, Failure: FIX                                        
Clock OK
Auxilliary Socket OK
Ignition Switch On PARK
Component                     Status  Note, Failure: FIX                                        
Tail Light OK
Front Parking Light OK
Instrument Lights OK Instruments Illuminated, All Indicator Lights Off
Volt Meter Light OK
Clock Light OK
Ignition Switch On START
Component                      Status  Note, Failure: FIX                                        
Tail Light OK
Front Parking Light OK
Instrument Lights OK
-Turn Signals OK Lights When Turn Signal Switch On
-Oil Pressure OK Lights When Engine Off
-Generator OK Lights When Engine Off
-Neutral OK On In Neutral, Off In Gear
-High Beam OK Lights When High Beam On
Volt Meter Light OK
Volt Meter Reading OK Shows +12 Volts
Clock Light OK
Turn Signals FAIL Each Side On, But Don’t Flash:
REPLACE TURN SIGNAL RELAY
Low Beam FAIL YELLOW Wire Broken In Left Switch:
REPLACE LEFT HANDLEBAR SWITCH
High Beam OK
Flash High Beam OK
Rear Brake Light FAIL Won’t Light:
BULB LOOSE IN SOCKET
Front Brake Switch FAIL Won’t Go Off. Washer Kept Plunger Extended When Lever Closed:
REMOVE WASHER
Rear Brake Switch FAIL Won’t Go Off. Plunger Stuck:
ALIGN SWITCH TO HOLE WITH SCREWS.
Starter Motor OK Just Bumped it, Didn’t Crank it
Horns OK
Clutch Switch FAIL Just Bumped It, Didn’t Crank It. Starter Works In Gear:
SWITCH BODY TOO WIDE. SANDED SIDES TO FIT SLOT IN PERCH
Kill Switch OK No Power To Coils Or Starter Relay.

Electrical Problems & Resolution

The following is a summary of the problems I found and how I solved them.

Turn Signals

The turn signals would light on one side, but not flash. I replaced the turn signal relay and that fixed the problem.

Low Beam

The low beam did not come on when the ignition switch was in the ON position. I removed the left switch assembly and realized a wire was missing, the YELLOW wire that sends power to the low beam filament. I had not noticed this before. Further exploration showed that the wire broke off the switch terminal and someone had poked  it up under the outer sheathing which is why I missed the problem when I removed the switch and inspected it.

BMW recently made the RT length left handlebar switch assembly available again and I  ordered a new one.

Rear Brake Light

I had multiple problems with the brake light circuit. I had not installed the rear brake pedal, so the brake light should be on, but it wasn’t. I removed the rear tail light reflector and found the bulb was not seated in the socket.

Front Brake Switch

I disconnect the rear brake light sub-harness so I can test just the front brake switch. Pulling the front brake lever did not light the brake light. The switch is normally closed since the edge of the brake lever pushes the plunger into the switch to open the switch. When the you pull the brake lever, the plunger extends all the way closing the switch so the brake light goes on.

I remove the handlebar switch and can make the tail light go off when I push the plunger and on when the plunger is fully extended. The switch came with a washer so I remove it so the plunger would extend closer to the brake lever. This fixed the problem.

Rear Brake Light Switch

I disconnected the front brake light switch sub-harness so I can test the rear brake switch. The brake did not light when I pushed the plunger on the switch. The switch is normally open and as the plunger is pushed into the switch It closes the switch lighting the brake light.

I removed the switch to test it and it worked. But I noticed that the plunger had to be flush with the plate on the switch bracket the plunger fits through. The plunger on this switch would catch on the edge of the hole and not retract far enough. There is some free play in the switch mounting screws so I carefully aligned the switch so the plunger would retract all the way. I mounted the rear brake pedal and tested the switch and it works.

Clutch Switch

I put the transmission in first gear and I just tapped the starter button. Nothing should happen, but the starter motor was energized. The clutch switch that is mounted on the left handlebar perch is normally closed. The clutch lever pushes the switch plunger into the switch opening the switch. So when the clutch lever is closed, the clutch switch is open preventing the starter motor from being energized when the transmission is in gear. When the clutch lever is pulled all the way it allows the plunger in the clutch switch to extend  all the way closing the switch so the starter motor can be energized when the bike is in gear.

DANGER:
Should the starter button be pushed while the engine is running, and the clutch switch does not prevent the starter from energizing, it can damage the flywheel and starter motor if the starter motor Bendix gear engages the teeth on the flywheel.

I removed the left handlebar perch and looked at the switch. It did not slide all the way into the slot in the perch. This would permit the plunger on the switch to extend all the way even when the lever is closed.

Clutch Switch Not Correctly Seated In Slot

Clutch Switch Not Correctly Seated In Slot

Clutch Switch Not Correctly Seated In Slot

Clutch Switch Not Correctly Seated In Slot

I installed the old one and saw that it slide all the way to the bottom of the slot. It looks like the body of the clutch switch is just a bit too wide to fit freely into the slot. I used 150 grit sandpaper on just the part of the sides of the switch housing that fit into the perch. The switch slide all the way down and the clutch switch worked correctly.

Clutch Switch Correctly Seated In Slot

Clutch Switch Correctly Seated In Slot

Clutch Switch Correctly Seated In Slot

Clutch Switch Correctly Seated In Slot

NOTE:
This clutch switch came direct from BMW. I checked another brand new clutch switch and found it was a bit too wide as well. It’s possible that the case is just slightly too wide on this batch of BMW clutch switches.

I’ll have to wait for the first engine start to verify that the charging system and optical-electronic ignition systems are working correctly.

Revisions

2020-08-14  Replaced tail light picture to show correct wiring to bulbs.

2 thoughts on “61 BMW 1983 R100RS/RT Install Electrical System

  1. First of all: You’re doing an amazing good job! Your description is better than the original workshop manual of BMW I own. But a remark. Never ever use spring washer or tooth lock washer. They are useless.Why? When I started my studies at the Technical University we learned machine design theory. One of the lessons was bolt connection calculation. Our professor teached us that these kind of washer are useless because they are weaker as the bolts. Also the force of the threads are higher then the spring washer. Neither the tooth lock washer nor the spring washer help not to loose the connection. Only the force (=torque) of the connection correct calculated saves from loosing. I didn’t belief him at that time. But over the years repairing many motorcycles and cars I made the experience that he is right. On every connection that looses I found tooth lock washer. I removed them, changed to normal washer, problem solved. There are helpful washers, developed later as my studies ended, like the “Special Rotor Bolt Lock Washer” you use ath the optical ingnition system. They are helpful and work. They are developed by Nordlock: https://www.nord-lock.com/de-de/nord-lock/
    BTW: On my BMW R60/6 I replaced the original ingnition system by Newtronic (former Pyranhia), GB, in 1994. It still works fine. It is good you change it. You will be happy and feel the difference. And also I restored my BMW in 1994 in the same way you do and remember all the things reading your description and see the pictures.
    Lupo (Germany)

    • Hi Lupo,

      Thank you for the information about locking washers. BMW uses a wave washer to lock the nut on the end of the stud that secures the horn to the bracket. The tooth washer does not lock the nut but is used between the metal strap and the horn bracket to keep the strap in place. I think that’s a reasonable use for the tooth washer in this situation.

      Best.
      Brook.

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