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 /5 series airheads.
Wiring & Electrical Disassembly
Since I’m going to powder coat the frame, I am removing all wiring and electrical devices from the frame. I took lots of pictures and labeled the wiring so it would be easier to put it back together. This information maybe helpful to you if you can’t remember what wires go where on your project.
This is the detail for the right-side handlebar front brake light assembly.
Coil and Harness Under Gas Tank
Here’s the coil wiring detail and the location of the wiring harness ties.
This shows the starter relay which has quite a bit of grunge on it and the wiring details. I’ll clean the cover up. With luck, it will continue to work fine.
There are two wiring bundles coming into the starter relay, one from the headlight shell (connects to the front of the relay) and one from the engine (connects to the back of the relay). I took some closeup detail shots of these.
I did a drawing of the wiring connections at the starter relay. Again, it will be months before I rewire things, so having a diagram is a great time saver. I noted which connections are from the front harness and the back harness and drew the diagram from the front side of the relay.
Here’s detail of the wiring loom the mounts on the frame spine tube. It’s rotting so it goes on the parts list for replacing.
Wiring Loom on Spine Tube
Here’s the detail of the engine wiring loom mounted around the frame tubes. This also has the red zip tie (not shown) that holds the looped wires to the frame.
This shows some details of wiring routing on the right side near the steering head and the voltage regulator.
Here are some detail of the plug that goes into the voltage regulator and some of the cable routing details along the frame spine tube.
Battery Ground & Speedometer Cable
Here is the view of the speedometer cable and battery ground cable mount to the transmission breather bolt.
The other two wires on the engine go to the oil pressure sending unit and the neutral switch. The oil pressure sender is on the left side, just rearward of the push rod tubes.
The neutral switch wire is bit more obscure. It’s a single wire that is mounted under a metal cover on the rear of the transmission housing. You can see the wire going to it just behind the left foot peg in this picture.
You can pry the metal cover off the transmission housing with a screw driver. There is a large brass button and a hard to see screw with a very narrow slot that is the set screw that attaches the wire to the switch. It was easier to get a picture below after the transmission was removed. The brass button is at the top, to the right, of the kick start lever.
This is likely anal retentive, but I took a picture of the battery wiring as well. This battery is for a lawn tractor and is mounted backwards so (+) and (-) terminals are the opposites sides of the bike from where they are on a standard BMW battery. I will replace the battery as this one has been sitting for six years and was originally installed in 1999 according to the markings. It didn’t owe me anything as I got 7 years out of it. 🙂
Tail Light Assembly
Now I removed the tail light and turn signals from the rear fender. These pictures are from my posts on the Silver Ghost, 1975 R75/6 build I did as there is no difference between the /5 and /6.
Now, I took apart the rear tail light assembly inside of which are the pigtails for the turn signals. I made another sketch of the wires inside the tail light assembly. I circled the terminals that had pigtails going to the turn signals.
Sub-frame Wiring Harness
I pulled the rear wiring harness out of the inside of the seat sub-frame tubing. It exits the sub-frame in front by the battery. If you push the rear end of the harness while you pull from the front and go slow, it will come out without tearing the outside insulation sheath.
Headlight Shell Cables
Back to the 1973 R75/5 pictures, this is a view from the bottom of the headlight shell showing cable and wiring harness routing.
So there you have it. If you need to look at how the major electrical components and wiring harness are routed and connected, these pictures should help jog your (and my) memory.
Next, I took apart the rear brake light and turn signal assembles to get the wiring harness out of the rear frame. You can see how to do that in detail in the beginning of the Silver Ghost Restoration-Part 11 Removing Sub-frame and Rear Drive post.
Here’s a picture of the wiring harness removed from the frame, but still connected to the headlight shell. When I remove the shell as part of post 31 BMW R75/5 Fork Rebuild, I’ll take the whole wiring harness off the bike with the headlight shell.
2019-02-06 Added Electrical System Resources section.
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Getting ready to do wiring harness… The pics are great. I made a ton of drawings as I removed old wires and I labeled everything.
Thanks. I took a lot of pictures to help route the wiring correctly when I put it all back together again. Drawings are a good idea, particularly for the terminals on the starter relay and voltage regulator. Best of success on the wiring.
Thank you (Molte grazie in Eyetie!)The picture of the neutral switch button on the end of the gearbox saved my day ! I thought I’d have to re-wire the whole bike, after a messy interference with the wires in the headlamp bucket: but now I see that maybe re-wiring from the neutral switch to the indicator will suffice. Here’s hoping….
I’m glad the picture was helpful. I’m hoping your solution avoids having to rewire the whole bike.
Your site has been enormously helpful in my ’72 /5 rebuild; the clear photography and step-by-step writing have guided me through many places where the various manuals just weren’t helpful. I’m almost finished, and can honestly say I couldn’t (or wouldn’t) have done it without you. Thanks so much for your hard work!
In an attempt to be helpful (as opposed to being an internet troll), I believe one of your images, “Battery Ground & Tachometer Cable Detail”, is mislabeled. I think that’s actually the Speedometer cable.
Cheers, and thanks again!
Thanks for the kind words and finding my mistake(s). I really appreciate it. I’ve made the corrections to the section heading, the content and the picture caption.
Hi brook! I been following your blog for a while now ever since I started on my r75/5 project. It’s been so useful! How do you remove the triangular plug off the voltage regulator? Is there a clip/catching securing it? I didnt want to just yank it off and break something.
There is no secret to this connector. Just pull while you wiggle it and it will come off.