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.

Wiring Harness Parts

I replaced most of the wiring on this bike. Here is a list of the new wiring harnesses I installed.

Part #	Description	Qty
61 12 1 244 138	WIRING HARNESS, BRAKE LIGHT SWITCH, REAR (from 09/80)	1
61 12 1 243 523	WIRING TRANSMISSION-SWITCH (from 09/77)	1
61 12 1 243 237	WIRING HARNESS TRIM – VOLTMETER/UHR	1
61 11 1 244 098	WIRING HARNESS SECTOR CHASSIS (from 09/80), Main Harness	1
61 13 1 244 090	WIRING HARNESS, BRAKE LIGHT SWITCH, FR (from 09/80), Front	1
61 11 1 243 646	ENGINE WIRING HARNESS (from 09/80), Voltage Regulator	1
61 12 1 243 216	BATTERY CABLE (PLUS POLE) (from 09/78)	1
61 12 1 244 475	BATTERY CABLE NEGATIVE, Included in EME BCK-475216	1
61 12 1 244 177	WIRE IGNITION COIL (from 09/80), Ignition Cntrl Unit	1

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.

• 61 BMW 1983 BMW R100RS/RT Replace Main Wiring Harness
• 61 BMW 1983 R100RS/RT Lengthen Handlebar Switch Wires
• 61 BMW 1983 R100RS/RT Routing Main Wiring Harness
• 32 BMW 1983 R100RT Install Handlebar Perch Assemblies

Charging System & Ignition System

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

• 12 BMW 1983 R100RS Install EME 400 Watt Charging System
• 12 BMW 1983 R100RS Install EME Optical-Electronic Ignition System

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.

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:

• 61 BMW 1983 R100RS/RT Routing Main Wiring Harness
  • Starter Relay Plug & Battery (+) Wire With RED End

Voltage Regulator

I show how I install the voltage regulator here:

• 12 BMW 1983 R100RS Install EME 400 Watt Charging System
  • Install Voltage Regulator

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.

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
BLUE–Red                      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

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.

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:

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
GREEN–White                (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.

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.

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.

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.

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.

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.

The battery box is ready to hold 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.

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

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.

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.

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.

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.

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.

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.

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.

The bracket was rusting in places and I repainted it.

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.

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.

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 waterproof.

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

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.

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
GREEN–RED                  Brake Light Power
BLUE–Red                      Left Turn Signal Power
BLUE-Black                   Right Turn Signal Power
GREY-Black                   Parking Light Power

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

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

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.

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.

I installed the old one and saw that it slid 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 slid all the way down and the clutch switch worked correctly.

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.
2021-05-09  Add wiring harnesses parts list.
2022-02-05  Correct typos.