Motorcycle Electrics 101 – a simple explanation of your bikes electrics
A lot of people can handle some minor component replacement. When you’re going a bit deeper on a custom bike ie. replacing the sub-frame, removing the airbox and side covers you need a little understanding of your motorcycle electrics. You’re going to need to do a fairly substantial re-wire. Old wiring looms are renowned for their problems and if you ask anyone who’s been there a total re-wire is your best option.
This guide will aim to give you some knowledge on the crucial components of your motorcycle electrics and help you select the right motorcycle parts. what they do and how they do it. In a later post, I’ll tackle re-wiring your bike, I’m still putting the simplified PDF wiring diagrams together.
My old man always told me, the best way to begin to fix something is to understand what it does. Firstly what does it do and second how does it do it. He also said if you can’t explain something in one sentence, you probably don’t know yourself. Here goes.
Electrical components
Stator-
The Generator for your motorcycle electrics. This provides the charge from your rotating crankshaft to the bike and battery. Simply put it rotates a magnetic component around a wire wound basket and produces power. Normally located on the left of the engine.
Regulator/rectifier-
Receives the AC charge from your stator, converts it to a clean DC to charge your battery, at between 13.5-14.5 v normally. If it hasn’t been replaced already get a new high-performance one. The original reg/rec on your bike wasn’t great to start with and if it’s 20+ years old, spend the money (they’re cheap) and get a replacement. Lithium batteries will not hold up under a shitty charging system, be warned.
Ignition switch-
Your keyhole, this is the first stop for your battery and cuts power to everything bar your starter relay. Minimum of 2 positions, first provides power to your lights and accessories second provides power to your coils and starter circuit. Check out the Purpose Built Moto handlebar switches now available in our store
Points/pulse generator –
Normally on the right side of the engine. This provides the timing for your Coils and spark plugs the pulse generator sends a signal to the CDI. Old bikes had magnetic points that wear out, you can replace them with a Dyna digital ignition which is highly recommended. Shown is a Yamaha RD engine where it’s located on the left side .
CDI or Capacitive Discharge Ignition-
This stores a charge from your battery in a capacitor, when the pulse is received from the points it sends a high power signal from that capacitor to the coils. If your bike is running horribly and nothing seems to be wrong with it, chances are it’s your CDI. These can be very hard to test though so chase down all other options before replacing it.
Coil-
These receive the signal from your ignition, amplify it and send the fire down the wire to your spark plugs.
Starter relay-
The starter relay takes a small signal from your button and closes a heavy duty switch, this pushes the high current to your starter motor. Your starter motor draws a lot of power, if all that power went through your start button it would melt and blow up.
Starter Motor-
Exactly what you think it does, This is the opposite of your stator, you feed it power, it will rotate and start your engine.
Indicator flasher relay-
In times of old, these were analogue timing circuits, with a capacitor. Your indicator flashes on, draws 30-46 watts and slowly charges the capacitor, once charged it turns your indicator off and repeats. With new LED lights, they draw 3-6 watts, this charges your capacitor a lot faster. This results in a very quick flash or a flicker in some cases, adding a load balancing resistor slows this back down to a normal pace. Newer flasher relays use MOSFET switching which is a digital solid state unit that is not load dependant and will flash at the same rate regardless of what lights you use. Purpose Built Moto has a flasher unit for use with handlebar pushbutton and LED indicators, it also runs your hi/lo beam using MOSFET switching.
Fuses
these protect your wiring from catching fire if overloaded or damaged. ever see a bikes wiring smoke up? The fuse probably blew and the genius just put a bigger fuse in it, it’s important to get your fuse rating right. Now you can get some really great 12v circuit breakers too which I tend to use on my builds, instead of replacing the fuse when there’s an issue you can reset it once the problem is fixed. If you don’t have an original wiring diagram to show the fuse rating I’ll show you how to work out your fuse rating too:
The formula is Power (watts) = Volts x Current (amps)
Or- Current (amps) = Power (watts) ÷ Volts
For a rough example, if you have 80w low 100 watt high beam 4 x 10 watt indicators and a 40 watt brake/tail light plus 20 watts of other lights.
You’ll have:
100+80+40+40= 260 watts
260 watts ÷ 12 volts= 22 amps maximum, use a 20 amp fuse or Circuit breaker.
Hopefully, you’ve picked up some knowledge and with knowing these few things, you’ll get a better understanding of what you’re doing when re-wiring your bobber or café racer.
Leave a comment below and sign up to our newsletter for our re-wiring tutorial and diagrams to be released soon.
Thanks for taking the time.
Tom.
Very useful tips Tom, I´m tryng to catch something to apply into my own project… I don´t know anything about nothing, but most of electrical wiring.
I´ll try to be patient and do it right with my little SR 250.
Big hug from an argentinian guy living in Barcelona 😉
Thanks Martin,
Hopefully it helps you finish your project right!
Make sure you email me some pictures when you finish
Tom.
Thanks Tom for taking the time to write and publish this interesting document.
Heard your interview on the American “Cafe Racer” podcast, sounded like you had a good approach so I looked up your site and there was a bike I’d seen on my favourite Aussie forum (2strokesdownunder) which a few of us on the forum had discussed with its owner, Locky!
Small world.
Love what you’re doing, even though your religion isn’t quite the same as mine 😉
All the best to you (just don’t chop TOO much off the old bikes!)
Regards,
Darwin (a Pom in South Australia)
Hey Darwin,
Thanks for getting in touch and for the kind words.
ever since I built that RD I’m hooked! got my heart set on a 2 stroke, I just have to find one.
Tom.
Hey man just want to say I love your site and builds!! definitely the best advice and explanations I have seen so far. I did have a couple of questions. I have a 1974 Suzuki TS250 that I am trying to convert into a scrambler. The only real mods, besides the lights and console, are that nasty real triangle I want to clear up. Where is the best place to put the battery and the oil reservoir (its a 2 stroke)?? and also is it possible to just spin the exhaust around to make a low slung pipe, or do I have to get a full custom system??
Thanks!
Hey Michael
Cheers for getting in touch!
The battery can be mounted in a small tray under the seat, being that old and a 2 stroke it should only need a small capacitor to hold charge. They’re easy to hide.
The oil tank you can make a feature of if you can build your own or simply get rid of it, blank off the oil pump and lines and run pre mix in the tank.
As for the exhaust, I doubt simply turning it over will work for you, you may be able to modify it but be careful. Look up “2 stroke exhaust litreage” to learn more about why.
Good luck with the bike mate, hope that helps.
Tom,
Awesome site! This article is in particular is helping me work up the courage to rewire my 1980 XR500 for a scrambler project. I don’t much about electrical systems, so well written articles like this one make it easy to read and follow along.
I’ve got a question though. Do you think it is practical to wire a battery into a system that previously did not have one? Looking to maximize certain comforts (grip warmers) and visibility (indicators and brighter lights). Didn’t know if rewiring the bike and putting in a battery might help out or not. Could be a misguided thought. Thanks again for the quality article!
Hi Jon,
Thanks for getting in touch.
Adding a small battery or capacitor is do-able but I would keep in mind 2 things.
1. Your reg/rec may need to be upgraded to charge the battery properly and make sure you match the voltage correctly. Some older bikes ran on 6V systems.
2. The battery won’t make your lights “brighter” as such, it will just even out the brightness and stop the lights from dipping when your bikes on idle, it also helps with LED lights to even out the voltage.
Good luck mate!
Thank you for these tutorials, this is exactly what i have been looking for. I am getting an inventory list ready for a complete rewire of my 83 cb1000c and was hoping you could give me some recommendations on parts. I am mainly unsure on which Regulator/rectifier and which flasher relay to purchase. I was originally going to attempt to reuse the ones on the bike but after reading your tutorial i am convinced that these are important items to upgrade. The price ranges for these are very large, and although i want to save money anywhere i can i don’t want to end up ordering something that i will regret.
Thank you again.
-Jacob
You can get decent Reg/recs from electrosport.com for nearly all types of bike. other than that it dependant on how you wire your control set up.
Have fun with it!
G’day Tom, great site and projects, thanks for being generous with your knowledge/experience.
I am hoping to take your advice re updating my Reg/rectifier on my Guzzi v65 project and wondering if you know of any Australian distributors of electrosport components?
Best wishes
Shane A
Hey Shane,
Glad you’re getting a bit of value from these posts! thanks for the feedback.
I don’t know of any direct for electrosport, However I am a dealer of Ricks Motorsport electrics that also sell high quality gear. If you can find the part you need from them I’d be happy to help you out.
Tom.
Thx, great content.
Hi guys,
Maybe you can help me.
I’m thinking of upgrading my 1978 xs250 to a lithium ion. I keep hearing you also have to upgrade you rectifier and resistor, no where can I find any specific information on what these upgrades are/specs they need/if they are compatible with my bike.
I’m a complete novice, Its a very simple bike, just bought on gum tree, its my first cafe racer, already been stripped back nicely. I’ve upgraded it from points to elec ignition and would like to do a couple of ground up improvements to it before I start dropping handlebars and sorting the seat loop….
It hasn’t got indicators so thats why I’ve been looking into the electrics, and the seat loop etc is related to that.
Can you help? Or send me to somewhere that can?
Anything would be appreciated.
Many thanks,
Fred.
Hi Fred,
Glad to hear you’re getting into your bike. All good questions to ask.
When you hear that you need and “upgraded” reg/rec that just means a replacement. The old regulators have a habit of spiking the voltage that will ruin the lithium battery.
Just buy a new replacement for your specific bike model and don’t get the cheapest option. You should pay between $70-100 I would think.
Plug that in and your lithium battery will stay happy.
Tom
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Hello,
First of all: Great site! Thanks for the tutorials. I’m starting to convert my Suzuki GN125 to a tracker and all these tutorials will be very usefull.
I’m going to rewire the whole bike. But one important question is still unanswered; “Which electribal cable thickness should I use in mm2 for the wiring?” My battery is a 12V8A gel battery.
Thanks
Wim
There’s a complex answer to this simple question.
The gauge of wiring is dependant on the load on the circuit.
Check out our other motorcycle electrics blogs for more detail on this problem.
Are 12v batteries always the way to go when u rewire your bike with, for example a motogadget m-unit? Or are there other options available. (Smaller sized batteries or lower voltage)
Hi Mate,
Generally if you’re upgrading the system, you’ll be upgrading the lighting.
If possible, I always like to do a 12V conversion on the bikes I build, it opens up more options.
I use antigravity small case batteries, theyre small and pack a good punch.
Tom
Good sight here sir, I’ve pulled all these parts off my ’83 Kawasaki, but now you’ve identified them for me. Now if you could just decide for me whether to make it into a brat, scrambler or a café racer
Glad to hear it Colin, Good luck with your project mate!
This is extremely useful. I am currently reducing a Goldwing to a Scrambler/Tracker type bike and the wiring was quite the item. However, I have followed the advice above and have had real good results. At this rate I will be riding come spring.
Merci….!
Couldnt be happier to read that mate.
I’m stoked you’ve got a little help from our article.
Tom
This article is so informative and helpful. I gather some important tips and informations to read this article.
Good Article , i Appreciate your work
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Thanks for your important knowledge