Motorcycle Electrics 101- Re-wiring your Café Racer or Bobber Project
Instructions and diagrams for re-wiring your Cafe Racer.
If you are planning on re-wiring your Cafe Racer and don’t know where to start, grab a seat.
Hopefully you’ve seen our post on what the electrical components do in your custom bike, or how to pick the right cafe racer parts. This article will show you step by step how to hook it all up and get your Café Racer or Bobber firing!
Things we will cover here:
- Parts you need
- Mounting your battery
- Charging/running circuit
- Lighting circuit
Parts you need
If you are still missing any of the parts for your build, make sure to check our custom pieces in our Online Shop.
If you’ve read our “how to build a café racer” blog the wiring should be one of the final steps on your build. I like to split this job in 2, you have a running/ignition circuit and your accessories circuit, with 2 separate diagrams. This makes the drawings simpler and if anything goes wrong it’s easier to trace the problem.
Before you think about wiring, mount everything on your bike from coils to your lights and speedo.
Battery mounting
Start by mounting your battery, and figuring out where your electrics tray will go. That should house your
- starter relay
- Black Box Control Module
- CDI
- Flasher unit
- Fuses or circuit breakers
Once that’s sorted mount the Reg/Rec either underneath or next to the battery. It needs airflow as it gets warm, so try not to put it in a cramped spot that’s fully enclosed.
Now you’re ready to start wiring. Some people prefer to run 1 wire the length of the bike and tap off for the active wires. In my mind this way tends to lead to a lot of joins and if one wire has an issue, your bike is going to have big problems.
I like to use a Terminal strip and join all the positive wires in the electrics tray. I separate the terminals into sections:
- Switching
- Lights
- Charging circuit
Shown below is our latest Black Box control module with optional accessories kit that includes a terminal strip and 2 micro fuse holders.
Using these accessories in your wiring is the simplest and neatest way we’ve found to make sure your motorcycle electrics run reliably while simplifying the job so anyone can do it.
I also always draw my wiring diagram, but I’m good with electrics so use mine to save you some time!
Get the PDF’s here: Wiring Diagram Download
Before you get going re-wiring your cafe racer, make sure you use quality connectors or solder joints and heat shrink your connections. With that done, let’s start with the charging/running circuit.
Charging/Running Circuit
- Run a black lead from your battery –ve to a clean bare metal part of the frame and bolt it on, this turns your whole frame into a ground. Also be sure to ground your engine/gearbox case at one point. Then run a red from the +ve to the starter coil. Connect the other side of your starter coil to the starter motor. This is done in heavy duty wire.
- Run a standard red 15A cable to the main fuse (20-30A) then to your key ignition. From the key ignition there will be 2 other cables; one goes to your charging circuit and coils, the other to a fuse for the lighting and accessories circuit (10-15A).
- Start finishing up your Running circuit, connect the 3 (normally yellow) wires from the stator to the reg/rec then connect the red to the battery +ve and the green to the –ve. Some bikes (Honda CB750s) will have extra cables to connect from the reg/rec to the coils. If not it will be included in the signal generator and CDI unit.
- Get your signal generator and CDI unit plugged in (or points), then run your blue coil trigger cables and connect the coils to your spark plugs.
Quick side note – if you would like to know more about motorcycle wiring diagrams, check out this article by bikezombies
That’s your charging and running circuit sorted, (the easy part) now work on finishing your lights and accessories. They’re already mounted up so the looming and connection is all that’s left.
Lighting Circuit
- You’ll have to run wires from your electrics tray to the front of the bike. I use a Black “snake skin” cable sleeving to protect my wiring from damage and it looks a lot better than your standard plastic wrap or electrical tape. as a minimum you’ll need;
Accessories
- 1 red active linked to the gauges, horn and brake switch
- 1 black ground wire
- 1 Purple for front brake switch
- Signal Lights depending on your gauges ( Neutral, Oil, Engine)
Lights
- 1 Blue for Low Beam
- 1 Yellow for High Beam
- 1 Green for Left turn
- 1 Brown for Right Turn
- Lights can be Grounded to the frame
Left Switch
- 1 green wire for rear left indicator
- 1 orange wire for the Horn
- 1 blue wire for high/low beam function
- All switches switch to Ground (black wire)
Right switch
- 1 brown wire for right indicator
- 1 yellow wire for the Kill switch
- 1 pink Wire for the Starter Coil (optional)
- All switches switch to Ground (black wire)
- Try to use solder connections on wire joins and good quality joiners for connection to switches and lights.
- Wire all buttons and install into switch housings, for in depth info on this check out our momentary switch guide
- Connect the headlight, and turn signals using the colours described above
- Connect your accessories +ve (gauges, brake switch, horn)
- Connect the other accessories wires as described above
- Connect any Dash lights relevant to your bike.
- All of your accessories will need to have the black wires grounded. You can connect this to the frame at any point or join them all and run a wire back to the electrics tray.
- With the cables connected, loom them into the cable sheathing and run them back to the electrics tray. Avoiding contact with hot areas or sharp edges.
- Now work from the rear of the bike back to the electrics tray (use snake skin here again). You’ll need:
- 1 red active wire for the rear brake switch, the running light, and the number plate light.
- 1 Purple switch wire from the brake switch
- 1 red wire for your brake light
- 1 green wire for rear left indicator
- 1 brown wire for rear right indicator
- 1 black earth wire
- The final step is to use your terminal strip to connect your wiring into the Black Box and linking the Horn and Brake lights up to their respective switches. The Gauges, Horn and Brake are run from a separate “accessories fuse” that’s not connected to the black box.
Now fire it up! I know there are simpler ways to wire a bike however in my experience, a little extra work here can save you heart ache if there is ever a problem. Simple fault finding is what I aim for.
I hope you’ve taken some good info away from this, again click here to download the PDF wiring diagrams I use for your own custom Café Racer, Bobber or Chopper project. Please leave me your comments below!
Thanks for taking the time and congratulations on completing re-wiring your cafe racer.
Tom.
Hi Tom,
I´m trying to customize my little Yamaha SR 250. Can I apply this simplified electrical scheme to my bike also? I´ve no idea about electrical stuff, I have it bare in its bones, but only watching to this mess of cables… it´s panic all over my brain!
Thanks a lot.
Regards
Martín
Hi Martin,
This is a general guide but yes I’m sure you can apply it to your SR250.
The best thing you can do is also find a PDF of your SR250 workshop manual.
Thanks for getting in touch.
Tom
Seriously helpful guide, no BS just simple, basic, hook this up to that. Perfect. Should come in handy when I tackle my XR’s wiring in the new year!
Thanks Kyle, Gald it was of help!
Hey guys! Great guide in helping newcomers in the cafe wiring world. My question is, in “Running Circuit” 2nd point, am I running the 15A wire from the +ve on the battery to the main fuse?
Hi Tylar, If you follow the diagram yes you link the battery to the main fuse. The size of the cable depends on your power needs, in most cases 15-20A should be ok. It depends on your bike.
Wish I’d seen this article before. I just spent $$ on an m-unit thinking it was the easy solution to rewiring my XT500 as I’m a dunce when it comes to electrics. Now I’m in a world of confusion trying to hook up my electronic CDI system which provides AC power to the lighting circuit and DC to recharge the battery from the coils at the flywheel. I’m thinking the whole lot will go up in flames. Thanks for sharing anyway.
Hi James,
I would urge you to look further into your bikes electrics, also read our other electrics blog which explains things further.
The M-unit is a good bit of gear although a little complicated. I’m sure you can figure it out.
Link to our blog:
https://purposebuiltmoto.com/motorcycle-electrics-101-explanation-of-motorcycle-electrics/
Tom
So I had just bought a 78 Cb400t hawk and have read that this bike is really hard to rewire? Am I reading miss information or what? I definitely want to clean up the triangle and this will definitely help. Is there anyway you could help?
Hey Mate,
The CB400N is no different to most 80s hondas, with a little patience and a wiring diagram you’ll have no worries.
If you need a workshop manual with wiring diagram shoot me an email. I’ll send it to you.
Hey. Thanks for the diagrams. My question is, how would I wire the bike without electric start, just kick start only?
Hey Tom,
Would you happen to have a wiring diagram for a 1998 Suzuki Intruder VS 800? I am having trouble finding one online but I intend to use the diagram you provided above with hopes that it will at least get me started in a positive direction!
Thank you,
Josh
Hi Josh,
Thanks for getting in touch.
I don’t have the wiring diagram you’re after sorry.
Your best bet is to buy or download a workshop manual for your specific bike.
Good luck with getting it all together.
Tom
Hey man love the simple wire diagram got something similar in my 82 gs450 was wondering if I can put all my grounds on one bolt in my drop pan under my seat (is welded to the frame)
Hi Devin
That’s fine, as long As the frame is well grounded to the battery and motor, and the stud is well grounded to the frame.you can use any number of points you like
Tom
What gauge wire should I use for the accessories and what size should come off of the battery posts?
Hi Steve,
The Gauge Wire should be dependant on what the accesory is. I generally will use 0.75mm2 cable for most everything.
The battery posts I believe are 10mm2 cable multistrand flexible.
hi tom i need to rewire my 1984 kawasaki z750 trike
im planning on using your wiring diagrams for the running system
and the lighting system
as these are the only circuits i need
would you possibly be able to advice what size and amped cables and how many different types of cables i will need to do this and what connectors are best to use
kind regards
david ross
if possibly could you email me the details ive asked for plus your basic wiring diagrammes with your step by step guide how to do it
ill antispate your responce
kind regards
david ross
Hi David,
Thanks for getting in touch. The information provided is general in nature and the specific cable size and fuxntiobality will be specific to your bike.
If you want the PDF downloads they are available in the “parts installation” of the site.
Tom
thank you for your assistants tom
I just discovered your website….not sure how I’ve been living in the dark so long. All of your info and articles are gold!! I’m currently rebuilding an 81′ XS1100 and I have it down to the frame. I’m trying to wrap my head around the electronic system cuz dang, it seems like french. I have the wiring harness still intact with things labeled from where I took them off. Assuming the wires are still good by checking things with a voltmeter do you tend to reuse them or just start from scratch and do all the wiring yourself?
Hey Steve,
I wil generally try to re-wire the whole bike. With the amount of gear you will remove/replace it end up being far quicker and neater that way.
[…] To learn more about the use and wiring of your push button switches, read our motorcycle electrics 101 guides here and here. […]
Hi Tom
Great article- thanks!
I’m the proud owner of someone else’s abandoned CJ360 Brat project. The wiring is a mess (two colors of wires…only).
Few Questions
1) The bike is kick start only – what do i need to address that?
2) what gauges of wire do you recommend
Thanks again
Hey Jon,
Stoked you liked the article.
With a kickstart only it means you need a lot less battery power. You can hide a tiny battery somewhere on the bike.
As for the gauge of wire it depends on what accessories you’re running.
I usually use 1.5mm cable for switches and small lights.
2.5mm cable for larger lights, grounding and the charging circuit.
Hope that helps.
Wow that was unusual. I just wrote an incredibly long comment but after I clicked submit my comment didn’t show up.
Grrrr… well I’m not writing all that over again. Anyhow, just
wanted to say great blog!
Really appreciate that mate!
[…] can take a look at our other wiring tutorials here. You can also directly download a PDF wiring diagram to help guide your project […]
[…] can take a look at our other wiring tutorials here, or check out the Purpose Built Moto YouTube channel for regular videos on building your cafe racer […]
Great guide, thanks for helping all builders out there!
I’ll try to wire my Zuki GSX750E 1981, but it has some weird Stator-to-headlight switch solution that’s gonna trip me up for sure 🙂
Wiring diagram in the manual is pretty good, so I’ll see where we go.
Good luck with your build mate.
What is that circuit board in the middle?
wondering that also
Hi Randall thats the Black Box Module:
https://purposebuiltmoto.com/product-category/control-relay/
Thanks Tom you are a lifesaver, thanks for making it easy with the pdf downloads! Thanks Jason
Glad theyre getting used mate.
What is that circuit board in the middle?
Hi Dave,
Thats an early version of our black box module, you can check it out here:
https://purposebuiltmoto.com/product-category/control-relay/
Hi there,
great information, thank you. would this work for my BMW r/80 ?
I appreciate your time, Thank you
Hi Tim,
This is a general guide, but will apply to any 12V motorcycle system.
Thank you very much for your help. 🙂
very helpful post.I like the way you briefly discussed the circuit part. I hope people will get benefits from this post.keep up the good work.
thank you
Completely agree – blinking lights in adverse conditions are difficult to judge distance with. Which is why I always run two different light styles in such conditions. blink for attention, and steady state for distance judgement and also potentially “to see with” depending on the route.
Nice Post
Tom,
In neither your charging circuit, nor the lighting circuit do you show a relay for the starter, or the headlight.
I am finishing wiring my bike now, and it has been proposed to me that I MUST use these relays, though I am not sure I do. The argument being made is the massive electrical pull of the headlight, and starter will over amp the headlight switch and kill switch.
I dont have much room for them, nor do I want to invest the additional time / money unless absolutely necessary.
What are your thoughts?
Hey Jason,
The starter motor I always use a relay, but the kill switch and headlight I dont.
2 reasons. All my bikes run LED lights with low amp draw and generally they run a black box module that has in built relays to handle that load.
Hope that helps man!
Tom
Hey Tom,
No doubt that is great writing, your article very informative and interesting. I have gone through entirely and each word, I appreciate your points of view. You’ve done a great job with making this clear enough for anyone to understand. Sometimes I was thinking to get over, but due to a heavy working schedule, I can not.
By the way, this has broadened my knowledge. Thanks for sharing.
Amazing post! For the first time i’m starting to understando how motorcycle eletrics works! English isn’t my native languege, sorry, could you explain whats that board between the Terminal strips on the picture?
Hey Alexandro,
That is the Black Box control module, it makes our button switches easily control you motorcycles functions.
you can check it out here: https://purposebuiltmoto.com/product/black-box-v2-lighting-control-module/
I got all my accessories before deciding to use a power distributor. Is it ok to wire this blackbox with switches that a not push release buttons? Everything seems like it would be fine as long as i release them. but I dont think Ill be able to get hazards going
Hi Mate,
Yes the black box is designed to work with momentary switches. your set up will work as it should, and you will also have the correct hazard function.
Tom
You recommend replacing the regulator/rectifier and say they’re cheap. Do you recommend a particular vendor? I see them on eBay around $30 US and at Ricksmotorsportelectrics.com for 3.5 times that. Any insite is appreciated.
We Use Ricks Regulators, Cheap in comparison to blowing up your batteries every few months!
Hello,
So, I have a question for someone out there. I am currently working on a motorcycle project right now and I am having to re-wire this whole bike. So, my question to anyone that can answer it for me is how do I ground the engine/gearbox to run a red +ve
You can ground the engine directly to the -ve terminal of the battery using a groundingt strap or large battery cable.
Hey there, awesome blog! Learning a lot of much needed information for my first Scrambler project. What did you make the under seat cable tray out of? Looks really clean, I’d like to make one myself. Thanks!
We use fibreglass normally, check out our blog on Building seats here:
https://purposebuiltmoto.com/custom-motorcycle-upholstery-seats/
Tom –
Your guide on rewiring was my Bible when I did my bike. Thank you.
I have a question concerning plug wiring. The plug wires on my bike, (motor, chassis, and drivetrain – Yamaha XZ550r (Vision)) have developed a short / bad connection, and plus, they’re 40 years old. As a consequence, I am going to replace the wires and caps. What do you usually do for new plug wiring on your builds? Any direction will be appreciated.
It’s always a good idea to wire and terminate new plugs on your bike, especially on the ignition and charging circuits as they can get dirty and hot causing corrosion a lot quicker than the lighting circuits.