- R80ST Wiring Diagram
- Video Summary
- Headlight Shell & Instrument Cluster Wiring
- Remove Electrical Components Under Gas Tank
- Removing Wiring Sub-Harnesses
- Remove Main Wiring Harness
I acquired this bike as a “project bike”, which means it was partially disassembled. The headlight, dash with the instruments and ignition, and the coil weren’t on the bike, so I don’t show how those are removed. But, I will show how they are installed when I get that far.
I indicate wire colors with all BOLD CAPITAL LETTERS for the solid color and Bold Initial Capital for the stripe color, e.g. GREEN–Black indicates solid green with a black stripe.
R80ST Wiring Diagram
This is from the Haynes manual. There are errors in many wiring diagrams, but I like the colored wiring shown in the Haynes manual.
The following video provides an overview of the R80ST electrical system.
VIDEO: 1983 BMW R80ST Charity Build: Electrical System Overview
Headlight Shell & Instrument Cluster Wiring
Although the headlight and instrument cluster weren’t on the bike, I will show the wiring that goes to those components.
The headlight shell on the R80ST does not include the wiring board that is common to many airhead models.
And, the turn signal relay and ignition switch are not inside the headlight shell either. All that’s in the headlight shell is the headlight assembly, with the headlight and the parking light bulbs.
Here are the loose wires at the headlight end of the main wiring harness that connect to the headlight, parking light, tachometer with indicator lights, speedometer, ignition switch, turn signal indicators, and the front turn signals.
The electronic tachometer contains the indicator lights for neutral, charging (aka GEN), low oil pressure and high beam. Therefore a number of wires go into it via a round plug the connects to the back of the tachometer housing.
Headlight Shell Wiring
The headlight plug was replaced so there are a number of splices that were not well soldered with a lot of electrical tape.
Instrument Cluster Wiring
The speedometer and tachometer attach to the top flange of the headlight bracket. Each has a strap around the body with two M5 studs that fit into the slots of the headlight bracket arm (see later picture of headlight bracket). The plastic instrument housing slides over the speedometer and tachometer and the bottom cover is secured with two screws, one on each side of the bottom cover. The instrument housing has a left and right turn signal indicator and the ignition switch installed in it. It also has two slots at the bottom and one in the middle for adding switches for optional accessories.
The ignition switch plugs into the dash and connects to the main wiring harness.
The turn signal indicator inside the instrument housing has a left and right arrow. The BLUE–Red is the left indicator and the BLUE-Black is the right indicator. There is also a GREY-Black wire that powers the speedometer illumination bulb. I’m missing the left turn indicator and speedometer illumination bulb sockets.
Front Turn Signals Wiring
The turn front turn signals fit onto a stalk on the bottom of the headlight bracket. The speedometer and tachometer mount on either side of the middle tabs at the top of the headlight bracket.
Remove Electrical Components Under Gas Tank
There are a number of electrical components under the gas tank along the right side of the spine tube. Some of the electrical components are shown in the picture below. The front of the bike is to the right. The components from right to left:
- Ignition Coil (Not Visible and Missing on This Bike)
- Plugs For Handlebar Combination Switches (Red, Black and White Plugs)
- Electronic Ignition Control Unit (Cooling Fins At Front)
- Voltage Regulator (Rectangular Silver Box)
- Auxiliary Relays (Small Grey Boxes, Not Stock, But An Option)
- Starter Relay (Far Left, White Bottom Relay)
- Headlight Relay (Far Left, Grey Top Relay)
- Turn Signal Relay (Not Visible, Under Headlight/Starter Relay Bracket)
- “Special Equipment” Plug (Not Visible, To Right of Headlight/Starter Relays)
- Fuse Box (Not Visible, Under End of Spine Tube)
On this bike, a previous owner installed two auxiliary relays on the voltage regulator bracket which has holes at the top for an optional twin relay socket. I think these were used to control driving lights as one relay has a YELLOW output wire and the other relay has a WHITE output wire.
I start removing the components under the gas tank starting from the front of the bike.
Remove Ignition Coil
The coil on my bike is missing. It mounts to the right side of the spine tube with two Allen bolts with wave washers. GREEN–Blue and BLACK wires connect to the terminals on the coil.
Remove Handlebar Combination Switch Plugs
The handlebar combination switches sub-harnesses have female plugs that plug into male plugs attached to a bracket welded to the right side of the spine tube under the gas tank. The left handlebar combination switch has two plugs, red and black, that plug into the corresponding color male plug of the main wiring harness, and the right handlebar combination switch has one plug, white.
The plugs have tabs on the top and bottom. I depress the top tab with a screw driver while pushing it toward the rear until I get the top tab past the edge of the hole. Then I depress the bottom tab in the same manner to release the plug from the rectangular hole in the bracket.
The plugs are plastic and if you press too hard on the tab, you can crack the plastic plug. DAMHIK :-).
Remove Electronic Ignition Control Unit
The ignition control unit mounts on a large shiny heat sink. The heat sink mounts to a bracket on the spine tube with Allen bolts and lock washers. The ignition control unit is Bosch part# is “0 227 100 103”.
The ignition control unit cable plug is secured to the ignition control unit with a wire bail. I use a screwdriver to carefully pry the bail out of the slot it sits in and remove the ignition control unit from the plug.
The cable with the ignition control unit plug has a large white plug on the other end that is part of the main wiring harness. I unplug the ignition control unit sub-harness from the white plug so I can remove the main wiring harness. The other end of the ignition control unit sub-harness goes inside the engine to the ignition trigger unit beneath the front engine cover.
There is a lot of corrosion on the back of heat sink that I will clean up.
Remove Voltage Regulator Bracket
There is a black plastic plug that fits into a socket with three pins in the bottom of the voltage regulator can. I remove it. The voltage regulator attaches to a bracket on the right side of the spine tube with two Allen bolts and wave washers under the voltage regulator can. The rear Allen bolt also secures a bundle of BROWN ground wires for the wiring system.
The Allen bolt connection to the ground wire bundle is critical to proper functioning of most of the electrical system so it’s a good idea to check that bolt to ensure it is tight and there is no crud or corrosion that will interfere with a solid ground to the frame.
Remove Headlight & Stater Relay Sockets
The headlight relay and starter relay plug into separate sockets attached to a bracket on the right side of the spine tube. The GREEN wires attached to the ring terminal are not stock. They bring power to the auxiliary relays mounted on the top of the voltage regulator bracket in front of the headlight and starter relay bracket.
The starter relay includes a diagram of the numbered terminals and a Bosch part number and manufacture date. It looks like the original starter relay was replaced. The terminal numbers are shown on the bottom next to the terminal.
The headlight relay has the terminal numbers printed on the bottom.
Remove Auxiliary Relays and Socket
It’s easier to remove the auxiliary relay socket after removing the headlight/starter relay socket. The auxiliary relay socket attaches to the top of the voltage regulator bracket with two screws. I remove the relays to get access to the screws. The relays are the same Bosch part number and are 5-terminal relays with two (87) terminals.
Remove Turn Signal Relay
The turn signal relay socket mounts to underside of the headlight/starter relay bracket with the same screw used to secure the headlight and starter relay sockets. The turn signal relay is missing on this bike. The wires to the relay socket come from the main wiring harness.
Remove “Special Equipment” Plug
This plug fits into a bracket on the right side of the spine tube and has a cover over the terminals. It has two tabs that secure it in the hole. Like I did for the handlebar combination switch plugs, I press on one tab and push that end of the plug past the edge of the bracket and repeat that for the other tab.
Remove Fuse Box
The fuse box is attached to the rear end of the spine tube with a large hose clamp. The power into the two fuses are on the left and the power out of the fuses are on the right. There is a thumb screw on the back of the fuse box that secures the cover.
The wires on the left side of the fuse box are GREEN on top and GREY on bottom. These bring power into the fuse.
The wires on the right side of the box are after the fuse. They are GREEN-Black on top and GREY-Black on the bottom.
Removing Wiring Sub-Harnesses
The main wiring harness attaches to several sub-harnesses that I remove.
Clutch and Brake Switch Sub-Harnesses
The handlebar clutch and front brake switches each attach to a sub-harness. The sub-harness plugs are behind the steering stem under the spine tube. The front brake switch has a GREEN–Red and BROWN ground wire and the clutch switch has a BROWN–Yellow and BROWN ground wire. Each sub-harness routes through the hole on top of the steering head gusset on the corresponding side the switch is on (clutch-left; front brake-right). I disconnect the sub-harness plugs and remove the sub-harnesses.
GEN Light And Starter Solenoid Sub-Harness
Next to the clutch and brake light switch sub-harness plugs is a large white plug with a BLUE and BLACK wire. The BLUE wire comes from the GEN light in the tachometer and goes to the voltage regulator and diode board. The BLACK wire goes to the starter solenoid inside the top engine cover. I disconnect it.
Neutral & Oil Pressure Switch Sub-Harness
A black plug near the left, rear of the frame connects the neutral and oil pressure switches sub-harness. The sub-harness routes along the lower left frame tube and is secured with several tie wraps.
The oil pressure switch is on the lower left side of the engine block behind the cylinder and has a BROWN–Green wire. The neutral switch is on the bottom of the transmission and has a BROWN-Black and BROWN ground wire. Due to the amount of oil around it, it’s clear the neutral switch leaked for awhile.
There is a ring terminal on the sub-harness that attaches to the lower left transmission mounting bolt to provide the ground for the neutral switch. I use a cut-off 8 mm Allen wrench to remove the transmission bolt as there is minimal clearance.
Remove Rear Lights Sub-Harness, Rear Turn Signals and Taillight
There is a large plug near the battery that connects the main wiring harness to the rear lights sub-harness. There is also a (+) battery wire in the main wiring harness with a ring terminal that goes on the (+) battery terminal along with the (+) battery wire that goes to the starter solenoid. My wire is missing the ring terminal.
The rear lights sub-harness routes along the left rear sub-frame tube and is secured with tie wraps.
The rear light sub-harness wires go to the rear turn signals and to the rear tail light assembly. The turn signal wires thread through the rubber turn signal stalk through a hole next to the mounting bolt.
I remove the turn signal lens to get access to the reflector. The turn signal wires attach to terminals on the back of the turn signal reflector. I remove them and pull the turn signal wires out of the hole next to the mounting bolt of the rubber turn signal stalks.
The turn signal housing attaches to the rear turn signal stalk with a clamp inside the housing. I loosen the bolts and slide the turn signal housing off the stalk. Then I remove the turn signal stalk mounting bolt to remove the rear turn signal stalks.
The taillight housing is already removed from the fender as I had to remove the rear fender to get the bike into my son’s truck to bring it home. The taillight housing mounts with two bolts and lock nuts to tabs on the rear sub-frame below the seat lock.
I remove the two screws securing the lens to get access to the reflector. I remove the wires from the terminals on the rear of the reflector. Then I use a small screw driver to push the rubber grommet out of the housing to remove the taillight wires.
Remove Rear Brake Light Switch Sub-Harness And Switch
The rear brake light switch sub-harness plug is on the right side of the spine tube near the battery.
The sub-harness is secured with tie wraps and routes down the right rear frame tube, over the top of the swing arm and under the swing arm gusset to the rear brake light switch that is mounted on a tab on the bottom of the frame’s swing arm bracket.
There is a rubber cover over the top of the rear brake light switch that the wires go through. The switch is secured with two screws and the wires are attached with two pinch screws. I remove the rubber cover, the wire pinch screws, the switch retaining screws, the tie wraps, and then the rear brake light sub-harness.
Remove Main Wiring Harness
The main wiring harness is secured to the spine tube with some tie wraps that I cut.
Here’s the main wiring harness with all the under the gas tank electrical components and sub-harnesses removed. I’m ready to remove it from the frame.
I pull the headlight and instrument wires through the gap between the steering head and the spine tube to remove the main wiring harness.
2022-12-07 Correct error in left/right handlebar combination switch plug on frame.
Love your detailed write ups! I am missing the “fuse cover with thumb screw” on my G/S, should be the same as yours, I need to find a replacement (or spend >$60 to buy the entire fuse block!). In case you plan to toss or sell any of the electrical components, please keep me in mind 🙂 !
Incredibly well documented work, as always! Can’t thank you enough, I’ve followed and read/watched just about everything from you. I have a quick question: is there a procedure to test a starter relay on the bench? The relay is from a 1974 R90/6. I have a condition of there being nothing that happens when I hit the start button,,,,battery is good, wiring contacts/grounds are good, before tearing into more I thought I would check the relay. Thanks much in advance
I’d start (no pun intended) by testing the starter solenoid and motor. Pull the top engine cover off to expose the starter motor and starter solenoid that is attached on the right side of the motor. The (+) battery cable attaches to a screw terminal on the starter solenoid. There is a spade terminal on the starter solenoid (usually with a black plastic cap). Pull that off the terminal on the solenoid. Take a piece of wire and carefully touch it to the battery cable and the spade terminal. If the starter solenoid and motor are okay, the starter motor will spin.
If the motor spins, it’s time to test the starter relay and the wires to the relay. I would clean the starter relay terminals and see if that fixes the problem. If not, I’d replace the relay.
I hope that helps.
Thank you for the speedy response, Brook, much appreciated! I will test the starter solenoid first thing tomorrow morning. Cheers and the all the best!
Hi, Brook, I tested the starter solenoid and starter motor as you advised. The starter did spin, that was a relief. I re-hooked up the starter relay just to se what would happen, again, nothing. Then I thought to pull in the clutch lever and hit the start button and the starter engaged!…..I took the clutch switch off the L/H perch and tried the start button and again the starter engaged,,,,I pushed in the “plunger” of the switch with my thumb, tried the start button and again, nothing,,,,,then, leaving the “plunger”, “extended” the starter engaged. this seems counter-intuitive to me when I mentally picture the switch installed in the perch.
The clutch switch closes when the clutch lever is pulled to the handlebar, so the plunger becomes fully extended to close the switch and is fully inserted into the switch when the clutch lever is not pulled.
You may have a bad neutral switch on the transmission. When you pull the clutch, you by-pass the neutral switch so the engine can be started in gear with the clutch disengaged.
Roger that, Brook, it now makes sense to me. As it turns out the wrong neutral switch is on the bike,,it’s a switch for later model R90/6 bikes,,,,mine needs one of an earlier version,,,,one is on order now. Thanks so much for your help!
Ah ha. Yes, that is a “gottcha” trap BMW created when they redesigned the transmission shift cam assembly. I’m glad you got the problem identified. I hope you put many happy miles on the R90/6 this season. 🙂