'homemade' wiring harness

gentlemens....I will soon be at the wiring phase of my 72 commando project...on my 68 BSA Lightning, 72 BSA Thunderbolt, and 72 Triumph Bonneville I made my own 'simplified' wiring harness and they work fine..for the Commando i plan to use 2 PVL coils, Podtronics, Pazon, sealed AGM battery, simple 2 position ignition switch, horn, and LED taillight..no turn signals or capacitor or anything else besides basic lighting and ignition...my question..i have the option of buying a full, 'stock' harness or doing it myself as mentioned...but I am somewhat leery of the grounding situation on Commando versus solid no rubber situation on BSA and Triumph...how I run ground wires on Commando if go homemade route? Thanks

My bike has a fairly heavy gauge cable – I couldn't tell you the gauge, but it's about 5mm of wound copper – attached to a head-steady screw into the cylinder head at one end and the appropriate terminal of the battery at the other, in my case the positive terminal, with a fair amount of slack. It's been on there a while now and hasn't failed yet. It's also discreet up there. It was just something I came up with while pondering what to do when I found that the earth connection from the main loom had failed – the bike had kept on running until I noticed the failure though! I'd be surprised if there aren't more elegant solutions …

alan hodge said:

but I am somewhat leery of the grounding situation on Commando versus solid no rubber situation on BSA and Triumph...

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It needs is a 'ground' wire connection to the engine.

Standard Commandos have a ground at the head steady plate so the connection is made to the 'engine' side of the rubber mounts.

Its an oxymorn to use factory loom and remain in any sense - minimalist. Besides signals they all come with half a shoe box of ground loops dead ends and useless supply wires for extra horns, sirens, lights and radio. I suggest relays for headlights and horn which if keeping Norton bar switches and head shell circuits - implies 4 relays. Also might think about a 5 amp audio power supply filter to the electronic ignition. Best place I found to bring all earth returns to a common firm conductive frame attachment was the center lower rear fender bolt. Also provide and screw down head shell Earth as blade terminals also seem too lose. I agree turn signals are not very effective/needed compared to handle signals and bright brake light. I'd use 3 fuses, main one at battery, then horn and head lights as only to protect the wires not the devices so no need for ign low draw. Some wires I want excess slack in like headsteady power unit and factory coil pack crisss crossing wires, I coil around a pencil to spring shape instead of just tucked in somehow.
Also might looking to art of loom lacing.

Grounds: you need a ground to the cylinder head, one for the headlight, and another in the headlight shell for all the indicators and signal lights, one for the tail lights and lastly one wire to the regulator rectifier. terminal from the battery to a point on the frame, and run all your grounds to the same point. Grounding done.
As per Hobot comment above the "factory" replacement harness has so much extra in it that is not used or goes nowhere. why even start there...

not sure how you can get away without signal lights, but in any case you have the experience already, go minimalist. i rewired right even out to the handlebar switch. if done correctly you can eliminate almost all the connectors. i would suggest you consider a least a 4 fuse panel.

I have always done my own wiring its easy if you have all the right tools, I use crimp connectors but have a a very good crimping tool that doesn't over crimp the connections, have never had any problems using them in over 40 years of diong wiring on British motorcycles.
There are plenty of wiring diagrams that simplify the wiring on our bikes, on my Norton now because I run a Joe Hunt maggie I only have 2 main power wires and 3 wires for brake and tail light etc, I have my earth wire outside of my main power wires and have a toggle switch hidden for ingition, a very simple wiring system that works great, make it as simple as you can and there be less problems.
When I use to have EI I always had a capacitor in the wiring system in case battery went flat, I have 3 points on the bike for earth, one to the head, one to the tail light and one to the head light shell and heat srink is your best friend lot better than just tape, make a wiring diagram with the wiring you only need to use and make it simple.

Ashley

For the wiring on my 500 single I used marine, "silvered" wire - minimises the chance of the Lucas-patented process known as the Green Death.
A bit dearer but, I believe, worth it.

Rob

In USoA signals were not required nor installed on '72's so still legal w/o them. Law changed a year or 2 after. Dealers and owners often installed signals for early Cdo on their own. My 1st March made Combat had signals my 2nd August came w/o and staying that way. All the weather proof clip together connections are so large compared to bullet clusters ya will have to plan head to stagger them to fit in tight area like under tank. I suggest many connections best with posi-locks, such as ignition trigger wires.

Alan , there is simplified wire diagram in britcycle catalog.... pretty sure it online too ... there are several , one includes EI , very basic and great starting point ... like Ashman I used the crimps with heat shrink , unlike him I use 2 position ignition switch and mostly walk away with key hanging off side of bike.... I went as basic as possible .... brake light , horn , headlamp and EI .... no relays just the one mini auto style fuse .... works fine .... a local restorer told me I devalued my nice bike by not using original harness , but really at this point , I try not to worry bout it ....

@alan hodge couple of thoughts towards your mission of simplicity:

Maybe consider a single coil with two outputs - with your Pazon you’ll be running wasted spark ignition anyway so there’s no reason why not, plus it’s tidier under the tank!

Your Podtronics doesn’t need to be earthed (the positive and negative side are terminated in cables). Run these straight to the battery terminals via it’s own dedicated fuse.
If you have an issue with alternator or reg/rec in the future, you are at least protecting everything else on the bike from damage.

so...the rubber isolastics don't have an effect on grounding wires? I was thinking they isolated each section of the bike electrically

Craig said:

simplified wire diagram in britcycle catalog.... pretty sure it online too ... there are several

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Here is one of several

I wired a couple of bikes from scratch, and really wanted to have color codes. I went to a wrecking yard and stripped out some sizable pieces of the wiring harness from a car. It seems to be getting harder to find wrecking yards any more. Seems like the large on-line guys are pushing out the smaller ones where they let you walk out back with a bag of tools.

ashman said:

I have always done my own wiring its easy if you have all the right tools, I use crimp connectors but have a a very good crimping tool that doesn't over crimp the connections, have never had any problems using them in over 40 years of diong wiring on British motorcycles.
There are plenty of wiring diagrams that simplify the wiring on our bikes, on my Norton now because I run a Joe Hunt maggie I only have 2 main power wires and 3 wires for brake and tail light etc, I have my earth wire outside of my main power wires and have a toggle switch hidden for ingition, a very simple wiring system that works great, make it as simple as you can and there be less problems.
When I use to have EI I always had a capacitor in the wiring system in case battery went flat, I have 3 points on the bike for earth, one to the head, one to the tail light and one to the head light shell and heat srink is your best friend lot better than just tape, make a wiring diagram with the wiring you only need to use and make it simple.

Ashley

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Ashman, could you possibly post a pic of your crimper or perhaps a make/model number? I tried one or two over the years and suspect I never spent enough to get a good one. I always went back to stubbornly soldering everything which takes about 5 times as long with no great advantage in the end. I'd like to join the modern era.

alan hodge said:

thinking they isolated each section of the bike electrically

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You are correct..however your SECTION= my ZONES
A lot of misinformation about the commando harness...
fact:
1. The electrical system grounding is entirely run through the red wires. The steel frame does NOT enter into the wiring system...
except:
2. within a local zone such as the engine to return HV spark and the points return current to the red ground wire at the head.
3. The commando has several local zones, battery, assimilator, headlight/front end, coil area, rectifier, zener, tail light, horn, accessory plug, and engine.
All these local zones ARE interconnected into a system with red wires...

sorry 4. Folks who disagree, unfortunately are ignorant of the engineering facts, and are probably proud of it...

Example: Take the drawing above with a ground symbol rather than showing the real interconnecting wire. very bad and incomplete tech help by ignoring the major concept of norton grounding which was your initial inquiry.

alan hodge said:

so...the rubber isolastics don't have an effect on grounding wires? I was thinking they isolated each section of the bike electrically

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To answer the first question, the only ground/earth that the isolastics affect is that for the engine, it needs its own earthing cable solely to give a complete and reliable path for the power to the spark plugs – if like me you have ditched points ignition in favour of an electronic system that needs no earth under the points cover. Nothing else is affected by the isolastics. Also to be borne in mind, though, is that things like the indicators [Edit: strike this bit, I'd forgotten that the earth for the rear light had simply failed internally on my bike, so it needed a new connection wired up: and the rear/brake light] don't have dedicated earths, but they should. DAMHIK, but easily sorted.

NortonMKIIA850 said:

To answer the first question, the only ground/earth that the isolastics affect is that for the engine, it needs its own earthing cable solely to give a complete and reliable path for the power to the spark plugs. Nothing else is affected by the isolastics. Also to be borne in mind, though, is that things like the indicators and the rear/brake light don't have dedicated earths, but they should. DAMHIK, but easily sorted.

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Again I mention bad advice.
If you don't have a red ground on the engine, an original commando will only run the points/coil ignition through the clutch cable...which has been proven to be intermittent.
All the equipment in the headlight/front end zone needs a red ground or else the headlight, indicator lights, and turn signals, current MUST run through the balls and races of the steering neck bearings.
If a technician does not have the capability to connect a tail light, brake light and rear turn signal to the provided norton system red ground then they should seek out a "competent" technician.

NortonMKIIA850 said:

Also to be borne in mind, though, is that things like the indicators and the rear/brake light don't have dedicated earths, but they should. DAMHIK, but easily sorted.

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While it's a PITA, I add a dedicated ground wire to the indicators. I just rough a spot on the outside of the socket and solder a red wire onto it. The only hard part is getting the wire through the stem if it is an original because the existing wire on those has thicker insulation. Newer ones use thinner insulation so getting a modern wire through is no problem. I've seen a few stems that one end is narrowed inside - I just drill them out. I also add a ground wire to the rear fender or to the rear/brake light socket depending on the bike and taillight assembly.

marshg246 said:

I also add a ground wire to the rear fender or to the rear/brake light socket depending on the bike and taillight assembly.

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What's wrong with the original norton/lucas red ground wire?
Improving the turn signal ground it's self is understandable.
The originals were chromed plastic and the ground can be problematic.

dynodave said:

Example: Take the drawing above with a ground symbol rather than showing the real interconnecting wire. very bad and incomplete tech help by ignoring the major concept of norton grounding which was your initial inquiry.

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While I agree with most of what you said, you should refer to the Norton wiring diagrams - they only show the earth (ground) symbol and make no mention of red wires or grounding the engine. Apparently Norton assumed that if you understood wiring diagrams, you knew enough to handle the omissions.

Some Triumph diagrams show the earth symbol as "Via Fixing Bolt" and that symbol with "Red" written beside it as "Earth Connections Made Via Cable". In other words, Triumph was clear that the frame was part of the grounding system. Norton is not clear but since the engine is electrically isolated from the frame, it's best to assume it needs a red wire ground.

My 1974 Commando MK2A did not have a ground to the engine and the harness is original as far as I know. I corrected that as soon as I got the bike. It did have a frame ground, rear fender ground, and a coil mount ground. My harness has all the Interpol wires but was not an Interpol bike.

On Triumphs, I add an engine to frame to red wire ground even though the engine is bolted to the frame. This ensures that it is actually grounded. Paint/Power Coat are insulators and I've found bikes with a low resistance instead of zero resistance between the engine and frame.