- Electrical System Resources
- When to Install the Harness
- Wiring Harness Preparation
- Video of Main Wiring Harness Layout
- Installation Details
- Installing Headlight Ears on Headlight Shell
- Installing Front Turn Signal Wires
- Routing Main Harness
- Routing Instrument Cluster Branch
- Connecting Starter Relay
- Connecting Voltage Regulator
- Connecting Coils & Dyna III Ignition Booster
- Routing Oil Pressure Switch, Neutral Switch & Rear Brake Switch Branch
- Routing Main Harness Through Sub-frame
In this write-up, I show the installation of the wiring harness, the voltage regulator, the starter relay and a Dyna III electronic ignition. This write-up does not show how to connect the alternator, diode board, points and condenser nor the starter motor wires. I had to remove these and install them when I replaced the timing chain and you can read about how to connect these electrical components in the following write-up.
I did not remove the harness from the headlight shell, so there is no information about making connections to the circuit board in the center of the shell, the ignition switch, the headlight relay or the turn signal relay. However, I did replace the left handlebar switch and wrote about how I did that. In that write-up I show a picture of the connection areas of the headlight shell circuit board and explain some mismatches between what you see in various wiring diagrams and what you see on the circuit board. Here is a link to that write-up.
The main wiring harness is not overly complicated. That said, I wanted to show how I install and route it on the frame and through the sub-frame. I shot a video to better illustrate the routing and layout and also took some pictures to show details about connecting the voltage regulator, starter relay and coils.
Electrical System Resources
I’ve been assembling information about the electrical system and have written several documents about it. You can find all my electrical system documents here:
Here the ones specific to the /6 series airheads.
When to Install the Harness
I chose to install the harness and associated electrical components when I had the engine, sub-frame, steering stem and fork tubes installed in the lower triple clamp. At that point, it’s time to mount the headlight ear that go on the top of the fork tubes so I can mount the top fork plate on the fork tubes, so it’s a good time to layout the wiring harness because the front turn signal wires from the headlight shell have to route through the headlight ears before they are installed on the top of the fork tubes.
Wiring Harness Preparation
Here is what the main harness looks like along with the headlight shell, the handlebar switches and the front turn signal and clutch switch wires. In the picture below, you see some white tags on various branches of the harness. I added these labels when I took the harness off so it would be easy to get each branch routed to the correct component.
There is a short wire harness that goes inside the rear tube that the turn signals and tail light mount to, and another short harness that connects the neutral switch on the transmission to a connector on a branch of the main wiring harness. There are pictures of these other short harnesses later on.
I clean the harness with soapy water and then let it dry for several days. I inspect the wiring for fraying around the connectors and repair and replace several that were damaged. I clean the metal connectors with electric contact cleaner. I use “Nitro Tape”, a water proof self-fusing tape to repair breaks in the outer plastic sheath. When wrapped around the cable, I can press the layers together creating a water tight seal.
Video of Main Wiring Harness Layout
The headlight shell has several wiring harnesses exiting it. The main harness exits from the bottom. The small front turn signal and clutch switch harnesses are just above it. Toward the top, on either side, the left and right handlebar control switch harnesses exit.
I shot this video to show how I routed the main wiring harness and fit it in the frame and the sub-frame of the bike.
I made some mistakes describing things when I filmed this video. So, I added notes that display in the video to correct the mistakes. Sorry about that.
I took some pictures that help show some of the details of how I installed the wiring harness, voltage regulator, starter switch and Dyna III electronic ignition and coils. The following explains what I did.
Installing Headlight Ears on Headlight Shell
I need to get each of the small turn signal wire bundles on the correct side of the bike. There is a bundle with a blue/red and a bundle with a blue/black wire. The blue/red goes on the LEFT and the blue/black goes on the RIGHT.
On this bike, each of the two small wire harnesses coming out of the bottom of the headlight shell include a brown ground wire.
I route the wires for the turn signals through the headlight shell ears and then install the ears on the top of the fork tubes. I loosely attached the headlight shell on the right ear with the mounting bolt so I didn’t have to hold it while working on routing the front turn signal wires.
I mount the headlight ears to the headlight shell and route the front turn signal wires through the small hole in ear ear and out the bottom of the ear.
Here is the left side hardware used to mount the headlight shell to the ear. The outside components are on the left and the inner most components are on the right. The rubber gasket goes on the inside of the ear next to the headlight shell.
In the picture showing the mounting detail below, I mistakenly show TWO rubber grommets, one between the headlight shell and the headlight ear, WHICH BELONGS THERE, and the second on the outside of the headlight ear underneath the wave washer WHICH DOES NOT GO THERE. My mistake when I took the picture.
The black plastic ring marked “Ignition” is on the outside of the ear and is secured with the large chrome nut next to it with the large flat washer under the nut and the wave washer under the black plastic “Ignition” ring. As shown in a picture below, the chrome nut has the beveled edges of the flats to the outside.
Once the ignition switch is mounted on the left headlight ear, I mount the right side of the headlight shell using the following hardware, again, the parts on the left side are toward the outside of the ear. One rubber grommet goes between the inside of the ear and the headlight shell and the other goes on the outside of the ear with the large chrome flat washer on top of it. I insert the bolt through the chrome washer and tighten it into the embedded nut inside the headlight shell.
Installing Front Turn Signal Wires
Here are the parts for mounting the headlight ears and front turn signal stalks.
At the bottom of the headlight ears is the larger diameter rubber bushing with cutouts that fits on the lower triple clamp. One cutout fits over the steel pin in the lower triple clamp and the other is used to route the turn signal wires into the turn signal stalk.
I route the wires through the hole in the headlight ear and out the bottom. I install the turn signal stalks so the one of the two cutouts are located over the pin in the lower triple clamp. The other cutout is used to route the front turn signal wires into the turn signal stalk via the gap in the lower fork clamp.
Then I install the larger rubber bushing into the bottom of the headlight ear and align the cutout over the metal pin in the lower triple clamp as I slip the ears over the two fork tubes.
I align the front turn signal wires around the fork tube and down through the cutouts in the large rubber bushing and the turn signal stalk. I push the wires through the turn signal stalk until the come out the end and pull them until this is a small amount of slack in the wire between the headlight shell and where it enters the turn signal stalk.
I install the top rubber bushing in the top of the headlight ears and ensure that the top of the fork tube is flush with the bottom of the top triple clamp. I install the top fork nut finger tight in both fork tubes. There should not be any binding of the top fork nut when finger tightening it. If there is, then the fork alignment in the triple clamps or the height of the fork tubes needs to be adjusted. There is a separate write-up on how I aligned the fork tubes so when I tighten the top fork nuts, there is no resistance.
I test fit the turn signal housings to be sure I have enough wire to connect to the bulb terminals. If there isn’t enough wire, I can remove the headlight chrome ring and feed more turn signal wire out of the headlamp and through the turn signal stalks.
Routing Main Harness
The main harness exits the headlight shell from the bottom. Shortly after exiting, there are a three branches that come off the main harness;
The one with the four push on terminals goes to the left side starter relay.
The second with the large rubber block on the end plugs into the back of the instrument cluster;
And the third branch (shown below) has four push on terminals (not shown in the photo but visible in the video) that go the front brake master cylinder. The two terminals at the end plug into the contacts in the cap of the brake fluid reservoir and the two near the branch plug into the front brake light switch on the front of the master cylinder.
I route the main harness so it goes under the bottom triple clamp.
The three branches exit the main harness just after the main cable passes the frame front down tubes. I push the main harness along with the three branches below the steering head and between the frame tubes that are welded to the steering head. The long portion of the main harness after the three branches goes along the bottom of the spine tube between the two brackets (voltage regulator bracket on the right and starter relay bracket on the left) welded to the spine tube.
Routing Instrument Cluster Branch
I route the branch with the large rubber block that plugs into the instrument cluster in front of the top fork plate and behind the headlight shell.
Connecting Starter Relay
The starter relay terminals connect with one branch from the main harness and also to a branch from the top of the front engine cover. I marked the relay terminals with the numbers shown on the wiring diagram and made up a legend with color codes, a sketch of the relay and a table of terminal numbers and wire colors.
Most of the terminals have two spades, one toward the front of the relay and one toward the back. I connect the wires from the branch of the main harness to the front terminals and the wire from the engine cable to the rear terminal and then I mount the relay to its bracket.
Connecting Voltage Regulator
The voltage relay has a “T” shaped receptacle on the bottom that the other wire coming from the top front engine cover goes to. I purchased an EnDuroLast electronic voltage relay from Euro MotoElectrics since the original relay has been in service for 40 years. I keep the original as a spare.
The blue square pad on the bottom can be used to adjust the maximum voltage the regulator will allow.
Connecting Coils & Dyna III Ignition Booster
As the remainder of the main harness continues along the spine tube, there is a blue/green wire and series of brown ground wires that exit the main harness near the coils. These go to the coils. I have dual plug heads on this bike and I mounted the dual secondary version of the red Dyna III coils. When I removed the wires, I labeled the coil so I can get the correct wire on the proper terminal.
The Dyna III ignition booster has a red wire that comes out of the booster and goes to one terminal on the left coil and the blue/green wire from the main harness goes on the other spade of that terminal.
The black wire from the booster is a ground and I mount it under one of the right side coil mounting Allen bolts. The brown wire goes to a terminal on the right coil.
In the picture above there is a black wire with a white label showing “O” on it. This is the black wire that goes to one side of the condenser under the front engine cover. It is connected to the other spade the brown wire from the booster is connected to. I connected this wire so if the Dyna III booster fails or the hall effect sensor that acts as the points fail, I can pull the hall effect sensor plate out, remove the magnet from the centrifugal advance unit, install the stock points plate with points and hook the other end of this black wire to the condenser and the points wire to the condenser. BUT … I MANAGED TO CONNECT THE OTHER END TO THE CONDENSER AS WELL!!!! When that happens, the bike will NOT RUN. In my attempt to be clever and avoid having to figure out wiring changes under the tank when the ignition booster or Hall effect sensor fails I outsmarted myself. 🙂
Routing Oil Pressure Switch, Neutral Switch & Rear Brake Switch Branch
A bit further along the main wire harness is the last branch. One branch ends in a bundle of wires without connectors that goes to the rear tail, brake and turn signal lights (I describe how it is routed later). The other branch has two branches in it: one has green wires that go to the rear brake light switch on the right and the other has a wire with a connector that goes to the oil pressure sender and a short branch with a connector that has a vertical and horizontal male spade that goes to the neutral switch on the transmission. This branch plugs into a short wire harness with a pair of wires that go to the neutral switch.
In this picture the branch that goes to the oil pressure switch, neutral switch and rear brake light switch goes down the inside of the left rear frame tube next to where the sub-frame bolts to the frame.
I route the branch with the green brake light switch wires under the battery box and over to the rear brake light switch bracket. You can see where it branches near the lower left frame gusset.
The other branch continues down the left lower frame tube toward the oil pressure switch on the engine. The oil pressure branch is the longer one and the neutral switch branch is the shorter one.
When you look inside the neutral switch connector you will see two female sockets, one vertical and the other horizontal. They plug into a short harness that has two wires that connect to the spades on the neutral switch. Here is a picture of the short harness that plugs into the short neutral switch branch of the wiring harness. You can see the vertical and horizontal spades inside the connector. The part number of the short harness is (61 12 1 358 107).
Routing Main Harness Through Sub-frame
The last part of the main harness includes wires to the tail light, brake light/running light and rear turn signals. It routes through holes in the sub-frame. I’ve used a coat hanger to pull the wire through the sub-frame from the hole on the left side near where it mounts to the frame. This time I used shrink tubing around the ends of the wires and sprayed a little WD-40 on the outside sheath and then pushed it through the sub-frame toward the rear hole. I grabbed it with needle nose pliers and pulled it through the rear hole.
These wires go inside the rear tail light shell. The tail light shell mounts on the base of the rear turn signal tube. There is a short harness that goes to each end of the tube with wires for the rear turn signals, part # (61 12 1 350 643).
The wires from the main harness and the rear turn signal harness connect to terminals on the back of the tail light housing. I made a picture of what terminals had which wires connected when I disassembled the bike.
Now that the harness is routed, I can connect it to the various components as I assemble them. When everything is connected and working, I use black wire ties to secure the harness to the frame.
2019-02-06 Added Electrical System Resources section. Allowed comments.
Hi there, I follow your blog diligently. Thanks for the hard work. In the wiring harness install video you point out a green wire from the main harness and a black wire also from the main harness going to the ignition coils. I am in the process of installing a new harness into my 74 90/6 and have also those two wires available but I have the suspicion that the black wire from the main harness is not used for this coil purpose. I got another single black wire from the engine harness that is connected (at the other end) to the condenser / points which in accordance with the wiring diagram would be the correct black wire. Would you agree? The black wire that is part of the main harness goes to the headlight and I can’t for my life figure out what that one would do. If any has any inside it would appreciated. Greetings, Heiko
You are correct that the black wire from the condenser goes to the outside terminal of the right coil.
In the 1974 bikes, there is a black wire that goes inside the headlight shell to the “H” terminal which is used by the horn. It comes from the horn button on the handlebar control so I don’t think that one is inside the main wire harness. The other wire from the “H” terminal goes to the horn.
I don’t know where you got the replacement main harness. On the 1975-1976 harness, there is a Black wire in the main harness. It goes from the starter relay, terminal (87) to the light relay, terminal (85). It is used to turn off the headlight when the starter is engaged. The 1974 bikes do not have a light relay, so if this is NOT a 1974 wire harness, that wire is not used and you can ignore it. The relay with this feature was added after the 1974 model year.
I hope that helps.
I hope that helps.
Thank you so much for your excellent work. It really helps those of us learning. Especially those of us who are a bit too OCD for our own good!
I’m working on a 1975 R75/6 barn find that I have never seen run. It came to me with a Windjammer fairing, and thus a real mess in the headlight bucket. After attempting to track down all the splices and wire replacements that the PO installed (original owner, thank God), I finally broke down and bought a new main harness from Euro Motoelectrics.
I carefully researched, unplugged the old/plugged in the new wires and soon had a new harness installed. I tested everything I could and all worked as they should. I then began work under the front engine cover. I installed new points/condenser and got it all timed appropriately following Boxer2Valves videos. Then I installed new alternator brushes and confirmed continuity of the alternator.
This weekend, I replaced the diode board and wires with the same ones you did from EuroMotoelectrics. I buttoned the whole thing up and started testing the electrics in preparation for attempting the first start (once my recoated gas tank has cured).
Everything seems to work fine until I get to the starter. The Neutral light is not on, unless I pull in the clutch. Then when I hit the starter button, instead of the starter engaging, I get a high-pitched beep that seems to be coming from the headlight bucket. It sounds like a VW Beetle horn, but very muted.
For the record, I have replaced the starter relay, voltage regulator, diode board, flasher unit, ignition switch and the starter motor/solenoid were recently checked and found to be fine. The neutral switch checked out about a month ago when took everything apart, cleaned and reassembled.
Any thoughts on where to start looking?
PS – again, I can’t thank you enough for your great work!
I happened to make a video about the neutral light, clutch switch and starter relay based on my 1983 R100RS. I believe the components and wiring is the same as used in your bike. That said, there is a mistake in the hand drawn diagram. I show the wire from the starter button going to the same terminal (86) on the starter relay as the two wires from the kill switch and the neutral light. The wire from the starter button goes to a separate terminal (85). But, the description of how the neutral switch, clutch switch and starter relay work is correct.
Bob Fleischer has a description of what happens when the diode at terminal (85b) fails (about 80% of the way through the document).
“The diode was to prevent the neutral lamp from indicating every time the clutch lever switch was activated. These diodes have been known to fail by SHORTING. If so, the neutral lamp will light up every time the clutch lever is used.
If the diode failed OPEN, the neutral switch will not allow starter operation UNLESS the clutch was pulled in.”
It sounds like this may be your problem. The bad news is, the diode is on the underside of the connector board inside the headlight relay so it’s a PITA to get to and replace.
You can use an ohm meter to test if it’s bad. It should have either, zero or infinite, ohms when the leads of the ohm meter are connected with red on one of the terminals on the left side of the 85b block and black lead is on a terminal on the right side. And it should show the opposite value (infinite or zero) ohms if you switch the ohm meter leads so the red lead is on a right side terminal and the black lead is on a left side terminal.
If the diode is bad, you could opt for a new connector board, or try to replace the diode as Bob describes in his article.
I do not have any ideas what the sound you hear is.
I hope this helps.
Thanks, Brook. I have a lot of troubleshooting lined up on this for the weekend. Something I actually look forward to because in the end, when the solution comes, there is nothing like the feeling. Have a Merry Christmas!