3C wiring

Paul Marx

Paul Marx

Hero member
Location
France
A helping hand or two would be lovely.

I've started wiring the 3C up. So far, neutral switch and rear light are wired in.
I purchased a loom from Motorcycle Wiring Specialists in the UK. http://www.motorcyclewiringspecialists.co.uk/services.html
It's nicely done but very basic. I'll certainly have to make up a few small sub looms to wire some components in. I'll need to do a bit of customising since the bike is gaining a Redax ignition and alternator kit with a regulator.
The original loom was a right mess since the ignition switch between the instruments served no purpose. The ignition switch with a key was under the seat.

It's a 1974 3C.
What I'd like to know is where do all the electrical components fit: fuse box, starter relay etc. Photos would be most helpful as would a description and if possible photos of how the loom winds its way from the battery compartment to the headlight. The loom I have, as the main part of the original loom, seem very long so there must be some bends somewhere.

How do I dispense with the engine stop relay?

Also, in the headlight, there are 4 wiring blocks. 2 yellow, 1 red and 1 brown. Do these colours have a significance? ie: red is live, yellow is switched live etc.

Any help much appreciated.

Paul
 
It probably would have been easier to start from scratch and make your own harness rather than buy one that's not particularly relevant to your bike. Especially since the original 3C electrical system was poorly designed anyway.

If you want to go ahead with the harness you bought, you'll need lay it out on the floor, unwrap it and make the following changes:

Firstly, strip out all the old alternator and CDI Ignition wiring. The stop relay wiring is part of that so it'll go too.

Create new sub-harnesses to accommodate the new ignition and charging system. Red's ignition and alternator system will have wire tails on the components that should be long enough to reach where they need to go, but you will need to make up some multi-pin connectors to plug it all together. For example, you'll a 6-pin connector (of suitable current rating) for the RR - 3 (normally yellow) phase wires, a (red) feed to the battery, a (black) earth, and depending on the particular RR, perhaps a voltage sensing wire.

The engine kill switch will need to be re-wired to cut the power to the ignition unit rather than switch the stop relay.

It's a bit cumbersome to describe the changes in words. Wiring diagrams are better tools for telling the story. As an example, I've attached a pdf drawing showing the stuff to get rid of. I could do other drawings showing how to wire in the new stuff, but I have other priorities at present. I may be able to do it in a week or two. If you think you need that level of help, send me a PM with your email address and we'll do it off the forum.

The fuse box on a 3C is under the left side cover. It was attached low down (near the bottom of the side cover) so it was out of the way of the side-access battery box. It was a shitty little thing that only held 2 ceramic fuses. If I were you I'd be putting in a fuse box with at least 4 blade type fuses so you fuse circuits that should have been fused in the first place.

The original location of bits and bobs isn't particularly relevant anyway. The battery compartment will be half the size of the original truck battery that the factory fitted. A much smaller modern AGM or lithium battery will free up space to put stuff like the RR and ignition unit, and you may want to change the location of other electrical components to make access more convenient.

Just remember, wiring is fun :)
 

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Hey Paul, When I rewired my 74 3c I made up a new battery compartment out of Tufnol, that gave me a back plate to mount the Ignitec box on, and space for two storage compartments.
Starter solenoid and regulator are mounted in front of the battery, behind the air filter, fuse box is mounted left side on a tab thats there.
You can mount your relays on the mudguard .
I like Tufnol cause its totally inert and you can work it with normal tools.
There is also a tool kit compartment behind the battery compartment.
Easiest way is just work your way through it, starting with the battery in its place, slowly it will all make sense.
I find it really enjoyable.

Here are some pics
Theres many ways to do it.
Hope this helps.
Tom
 

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Thanks for your comments, some useful.
Thanks Tom for the pics. Made me realise that I had an original starter relay. I was going to junk it and replace with some Japanese thing from ebay.
Thanks Dellortoman for the diagram, it will nicely complement what I have and every little bit helps. And you're right. I would have been better off doing the whole loom myself.
I know how to swim but still don't dare jumps in at the deep end.

Paul
 
Wiring loom on my 3C has evolved over 30 years, still a mess in the headlight. One day I will strip it all out and start again. The 3CL I just did and it is working ok. The start from scratch loom on the SF2 loosely followed the green book at the start, then I just changed it all to suit. Nothing is standard on any of my bikes. Not much help to you Paul.
 
If it were mine I would start from scratch as Cam suggested. I had the pleasure of sorting the rats nest in my headlight shell but I tremble at the prospect of having to change the bulb and not being able to stuff the intestines back into the cavity! For it's time I guess the terminal strips and numerous jumpers simplified things by running most everything into the housing and protecting the connections from the weather. But you are changing a good bit of the important bits and won't need all that wire in the headlight. Also it would give you the option of adding power relays to take the current load away from the bar switches and provide full power to the lights. The Motogadget M unit looks very interesting as it includes the relays etc. in a compact easy to mount package.
 
wdietz186 said:
If it were mine I would start from scratch as Cam suggested. I had the pleasure of sorting the rats nest in my headlight shell but I tremble at the prospect of having to change the bulb and not being able to stuff the intestines back into the cavity! For it's time I guess the terminal strips and numerous jumpers simplified things by running most everything into the housing and protecting the connections from the weather. But you are changing a good bit of the important bits and won't need all that wire in the headlight. Also it would give you the option of adding power relays to take the current load away from the bar switches and provide full power to the lights. The Motogadget M unit looks very interesting as it includes the relays etc. in a compact easy to mount package.
Click to expand...
Reports on the Moto gadget from Grant Duguid who used them on his restorations at one time is not good.

I shall persevere in the course I've chosen, the ready made loom , but it's not impossible that I stop and start from scratch.

Paul
 
As Cam said uncover your new harness fully or certainly at the ‘junctions’ so that you can pull unwanted wires out, but lightly tie wrap/tape the wiring together as it was supplied so that you don’t lose the gist of what the supplier had provided as much of it may suit as is. (It may well be taped together under the sleeve at various points already)
Before doing anything further decide on the location of all electrical components and mount them. Improvements such as relays to the headlight would be best done now too. It doesn’t hurt to use the ignition switch to only energise a relay which then feeds the rest of the bike.
Without telling granny how to suck eggs mount the regulator/rectifier somewhere in air free of heat.
Try your loom to this and see where it works or fails, decide whether to extend any short wires or try a new location for the component they’re not reaching.
Leave any wiring you can a bit long and don’t fit any connectors until you’ve fitted any sleeving. I like the expanding mesh sleeve with heat shrink or self amalgamating tape over the cut ends, others will have their own preferences.
Only look at one circuit/wire at a time it’s less overwhelming.
Don’t forget earth circuits!
The wiring passing the headstock needs careful running and it’s sometimes better to split it up into a few more flexible smaller bundles than have one thick lot.
For connecting I like molex as used on Guzzis for multi plugs or else non insulated terminals with soft pvc covers either jap size 3.9mm bullets or 6.3mm blades. The correct crimping tool for these is not expensive. (See MP71 vehicle wiring products website)
 
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Paul Marx said:
Reports on the Moto gadget from Grant Duguid who used them on his restorations at one time is not good.

I shall persevere in the course I've chosen, the ready made loom , but it's not impossible that I stop and start from scratch.

Paul
Click to expand...
Motogadget has given me and my friends no problems at all. I think people can have good and bad experiences with anything.
 
Surely it can't be that hard to bypass the M-gadget and go through the LH switch first? Adds wiring of course, which is what is supposed to be eliminated.
 
Dellortoman said:
I think Grant's main gripe was that Motogadget doesn't let you switch the headlight off. He had to put in a bunch of relays to make the headlight on/off switch work.
Click to expand...
that probably comes from set up, you have the choice when setting up the unit, you can make the thing do pretty much what you want it to do , you can even program it so that the indicators , if you use them or if they are fitted , turn off after a user chosen interval, eg 3 seconds, 4 seconds etc , you can have the indicators start with slow flashes that increase the longer the indicators are left on. I have found the moto gadget really a godsend for setting things up easily. Im not of the generation where everything is relays and solenoids etc, even though my vehicles have them, the moto gadget system lets me do things in a more modern approach, and more inline with the technology that I understand. Yes I havent learnt a skill from older technology , and i dont rubbish that older technology , but I dont see any problems with the moto gadget gear. If anything it simplifies wiring and reduces wire sizes and in terms of lighting, current draw by allowing led's to be used for everything, . That said I havent tried to mix and match old school electrics with new school. I did use a headlight on my morini 500 that had both LED and a normal halogen bulb, and I had no issues there with being able to turn the head light off and on.
 
Grant asked me for help with it at the time. I went through all the M-Unit programming options in detail and there was no way to switch the headlight off. It would only to switch between high and low beam. Although I've since heard a rumour that headlight on/off facility was incorporated into a later version. I haven't confirmed that for myself though.

piranha-bro2 said:
Surely it can't be that hard to bypass the M-gadget and go through the LH switch first? Adds wiring of course, which is what is supposed to be eliminated.
Click to expand...
No, there's no way to employ the light switch before the M-Unit. The thing only has a single 12V input that powers all of its various functions. But I drew up a circuit for him using relays in the high and low beam circuits after the M-Unit.
 
Dellortoman said:
Grant asked me for help with it at the time. I went through all the M-Unit programming options in detail and there was no way to switch the headlight off. It would only to switch between high and low beam. Although I've since heard a rumour that headlight on/off facility was incorporated into a later version. I haven't confirmed that for myself though.


No, there's no way to employ the light switch before the M-Unit. The thing only has a single 12V input that powers all of its various functions. But I drew up a circuit for him using relays in the high and low beam circuits after the M-Unit.
Click to expand...
This is from one of the moto gadget gurus on the

SOHC/4 Owners Club Forums​

"The head light will be activated automatically after pressing the start button or (for kick start) after one short light switch operation. If a push buttons is used for high/low beam control, a short push will toggle between high and low beam. Hold the button for 2s will switch off light completely. Press the button again will switch low beam on again. If a switch is used for light control it is only possible to toggle between high and low beam once the light is activated. " this is dated 2015

I didnt use standard switches on the clip ons, I have been told that perhaps the head light cant be turned off using the traditional rocker switches on older bikes.

So I think you are spot on there Cam, but if you change to the moto gadget or similar style switches you can turn it off , as I can on my Morini that I did with a first series m unit I dont think the later model blu came out till about 2017 or there about. I dig that people wont want to change the appearances of their switch gear. So they are great for me, but not someone that wants to keep a classic looking set up
 
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