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Discussion Starter #1
With Stuart’s much appreciated help I’ve now ordered all of the bits I need to re-wire my bike over the coming winter months. Initial outlay has been quite a bit more expensive than buying a pre-made harness for two reasons, a) I’m starting from scratch and have absolutely nothing in the garage to do this job and b) I’ve made allowances for the inevitable mistakes, I’m in over my depth.

This thread might be useful for others so I’ll update it with progress (and I’m sure lots of stupid questions) but for now an interesting fact is that there are 17 different colour combinations of wire needed to replace the original harness.
 

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Discussion Starter #2 (Edited)
As the first batch of re-wire parts arrived today I thought it best to try and familiarise myself with the wiring diagram and this has lead to the first of what I'm sure are dumb questions.

I've read about running discreet earthing wires (red) from the indicators but what about the rest of the components which are earthed? For example all of the lamps in the headlight are earthed and if I run a separate wire from each one that's a lot of red wire which has to find it's way back to the battery. Is it good practice to try and eliminate the frame as the earth conductor as much as possible, how practicable is this?

Secondly, I've bought some more fuse-holders to supplement the existing one to the negative battery terminal. Again I've read here that it's sensible to fuse other circuits but which ones and where would the fuses go?

Thank you
 

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I'm sure you'll get replies from people with a lot more experience on old bikes and I have, which is zero, especially positive Earth.
But I do have a lot of electrical experience, from a quick glance at the wiring diagram you only seems to have one main fuse, the reason multiple smaller fuses are fitted to separate circuits is called discrimination, so a fault in one circuit only blows the fuse for that circuit and leaves everything else working.
I would recommend at the very least fusing the lighting and ignition circuit separately, you obviously have to calculate the correct fuse size, you could use inline fuse holders which take up very little room.

As far as the separate Earth wires go the main reason for running separate Earth's is if you have an unreliable connection through the frame, for example if you connect to an earth on the headlight the current has to travel through the headlight bolt to the bracket and then the bracket to the frame through the headstock bearings and so on back to the battery. For components that are Earthed around the main body of the frame I don't see any problem, you obviously need to ensure good clean connection to the frame and maintain them.

For things like rear lights and indicators it's normal to run a short Earth wire from the light to the nearest point on the frame were the unit mounts to, therefore by-passing the bolt or fixing, you don't have to run every separate Earth wire all the way back to the battery.
 

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As scotty says, it's really a return (earth) from tail to somewhere near the indicators, then to the battery.
From indicators into headlight, from headlight to battery.
Engine to battery.
So not a massive amount and all singles until you get near the battery
 

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Hi Rusty,

:) Pleased I could help.

Initial outlay has been quite a bit more expensive than buying a pre-made harness
Bear in mind that, unless your bike was absolutely bog-standard electrically, you'd still have had the expense of tools, some terminals and wire to modify any pre-made harness. Also, apart from British Wiring in the US (and apparently even them not always), every other harness maker at best copies all the the cheapo compromises 'original Lucas' put in every '71-on harness; some (guess who?) add a few more of their own ...

The nice thing about your bike's harness when you've finished is the only compromises it'll include are the ones you put in. :) Plus you'll have the tools and a few spares for the next project ... :D

I’m in over my depth.
You aren't, trust me. :) Might look a bit daunting now but, as long as you continue to work methodically, it'll appear much clearer quickly.

One of the 'moments' I remember from my first rewire was when I'd stripped off all the black tape ... then there was the wiring diagram in Glorious Technicolor. :thumb

The other thing I didn't do on that first rewire but I've done on a few subsequent is copy and blow up the wiring diagram to a larger paper size, have the local print shop run off a copy, go over the black lines with coloured pens or felt-tips, pin it on the garage wall by the bike and tick off the wires as you install them. Or, if you're more computer-savvy (or have a bribable teenager), knock up a full-colour copy of the diagram is one of the myriad circuit-drawing computer packages?

I've read about running discreet earthing wires (red) from the indicators but what about the rest of the components which are earthed? For example all of the lamps in the headlight are earthed and if I run a separate wire from each one that's a lot of red wire which has to find it's way back to the battery.
Uh-uh, remember what I pm'd you? One 8-way (4 wires in each end) bullet snap connector inside the headlamp shell, another somewhere under the seat. Then individual component Red wires run only as far as the nearest 8-way. Using your list: Red wires from headlamp, pilot, two indicators, main beam idiot lamp, speedo. 'n' tacho. illumination run as far as that 8-way snap connector inside the headlamp shell; that's seven Red wires, the eighth is the 28/0.30 Red wire that'll connect to engine and the other 8-way under seat; a Red wire from the latter connects (through the main fuse) to the battery +ve terminal.

Is it good practice to try and eliminate the frame as the earth conductor as much as possible, how practicable is this?
Unless your bike has a non-standard harness now, when you strip off the existing tape or cloth, you'll see it already has Red wires to pretty-much every electrical component mounted certainly on cycle parts (bar the indicators). Lucas had by-and-large eschewed "the frame [any cycle parts] as the earth conductor" for many years before your bike was built.

For this reason, I never incorporate any cycle part as any part of an electrical circuit - e.g. a short wire from a component to the nearest part of the frame; it's certainly what the Japanese makers have done for decades ... and ime it's simply never long-term reliable. :(

Spark plugs and oil pressure switch do use the engine as an earth conductor. While it'd be possible to eliminate even that with a Red wire to each mounting, in practice, I've found one Red wire attached between the harness and somewhere on the engine to be fine for all electrical components on the engine.

I've bought some more fuse-holders to supplement the existing one to the negative battery terminal.
Uh-uh. You need to be absolutely crystal-clear about this because it's important.

Because the electrics are 'positive earth', the main fuse should be in the one-and-only Red wire attached to battery positive.

This protects against the not-unknown possibility of something metal accidentally touching the battery negative terminal itself and some other part of the bike. In this event, because the bike's electrics are 'positive earth', any metal parts of the bike can form a conductor to any wire attached to battery positive. If there isn't a fuse in the one-and-only Red wire attached to battery positive, this becomes an unfused short-circuit and damage will result very quickly. :( A fuse attached to battery negative cannot prevent this short-circuit because the short won't be through it. :(

The only exception I'll use is the +ve wire from an electronic ignition 'box', which I also connect directly to battery +ve. I don't put a separate fuse in this, on the basis the wire's either fully-insulated from the 'box' or, if it has to be extended, extension and connection are also fully-insulated.

I've read here that it's sensible to fuse other circuits but which ones and where would the fuses go?
I connect the DC wires from the reg./rec. directly to the corresponding battery terminals. Ime and mho, the reg./rec. -ve wire should not be connected to a break in the Brown/Blue wire (as the original rectifier and Zener were), the reg./rec. +ve wire should not be connected to the bike's other Red wires, definitely not to another sundry bit of bike. :eek:

If you accept that advice, then put a fuse in one of the wires between reg./rec. and battery.

Beyond that, fusing individual circuits is definitely desirable, but vexatious to actually implement ... :bluduh

The primary problem is most individual circuits diverge inside the headlamp shell - a White wire runs from an ignition switch terminal to supply: ignition (via the handlebar kill switch), oil pressure idiot lamp, brake lamp switches, indicator relay, horn and headlamp flash buttons; Brown/White runs from an ignition switch terminal to supply the Lighting switch, which supplies headlamp, pilot lamp, rear lamp and speedo. 'n' tacho lamps. Eight fuse holders crammed inside the headlamp shell ...?

Fwiw, I:-

. fuse an electronic ignition, but near the 'box', usually under the seat;

. because I use relays to switch the headlamp, and relays that take a blade fuse are common, the headlamp ends up fused.

Apart from them, potentially anything connected in any way to battery negative (on a 'positive earth' bike) might cause the main fuse (connected to battery positive) to blow and bring the bike to a halt in darkness. As it's my arse on the line, I do the best wiring and connecting I can.

Hth.

Regards,
 

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Rusty

I was in your position about 18 months ago. Burnt out wiring on my 5Ta. The PO had upgraded to 12v, fitted EI and a number of other upgrades so the standard harness was no use. I had basically no experience with wiring and was a bit daunted, but yer man Stuart patiently took me through it and eventually I got a wiring loom through his quality control, including adding 4 additional fuses. Once done I got it printed off A3 in a colour printer and laminated it. I built the loom over a few days and it worked as it should (well a wee hiccup with the pilot bulb soon sorted) and was still going strong when I sold it.

I am by no means competent, but once I got my head round what Stuart was saying I felt less dread and began to relish the challenge. Believe me matey, If I can manage it, most folk could
 

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Discussion Starter #8
Uh-uh, remember what I pm'd you? One 8-way (4 wires in each end) bullet snap connector inside the headlamp shell, another somewhere under the seat.
Yes I do and I have bought them. Of course the metal sleeves inside are all connected so will accommodate any combination of earth wires, for some reason I thought it had to be four in one way and four out of the other :Darn. An indication of my electrical competence, I'm much better at fishing and table tennis.

Out of interest why did Triumph (Lucas?) adopt a fuse in the negative side of the battery?
 

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Hi Rusty
You will be just fine, it might look daunting but if you look at the wiring diagram in sections, you soon realise it is a lot of very small 1 and 2 wire systems connected together by a battery and ignition switch. Just complete the small systems one by one and it will soon be done.
If you have any doubts about anything, Stuart will soon be able to get you back on the correct path.

Best of luck.
Peg
 

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Hi Rusty,

why did Triumph (Lucas?) adopt a fuse in the negative side of the battery?
:nod It was Lucas that supplied all harnesses about '68-on with the fuse fitted in the Brown/Blue wire attached to battery -ve (and then '79-on with the fuse attached to battery +ve, but 'negative earth' electrics :Not again).

It's one of the things I wish I'd been clever enough to understand the significance and ask the question when 'original Lucas' was still around, because I've never seen an internet forum explanation that made any sense. :(

Speculating - Afaict, there wasn't any fuse when 6V electrics were the norm (pre-'65/'66); :eek: the early 12V parts books illustrate the fuse/holder separately; when a fuse kept blowing, the paddlers at the shallow end of the gene pool were easily substituting just a piece of wire, then complaining when the bike went up in flames ... :Darn So Lucas modified the wiring harnesses to build the fuse into the Brown/Blue wire - designers and engineers must've been well-aware already the single fuse was a compromise, but the motorcycle makers wouldn't pay for multiple fuses so what did one more compromise matter? However, I appreciate the logical fly in that ointment is the fuse/holder could just as easily have been built into a single Red wire from a loom to battery +ve ...

Hth.

Regards,
 

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Discussion Starter #13
The second and final batch of parts arrived today so I’m all set to start. The quality looks very good, particularly the Autosparks bullet connector sleeves. They’re made of heavier gauge material than the ones on the aftermarket headlight loom fitted to my bike. A couple of connectors in my headlight fractured and I had to bodge with pliers as the bullets wouldn’t stay in.

The fuse-holders are larger than I thought they’d be and as Stuart has pointed out they are wired red, ok for the main fuse but if I use them on other coloured wires I’ll cut back the red wire as far as I can before attaching a connector. I did buy a 6 fuse box too just in case I thought of a better way of doing it.

A bonus is that I found my old RS Components cable stripper in the shed. This dates back to the eighties and while it looks tatty a liberal soaking of WD40 has got it working very well, that’ll save loads of time. So following the instructions which came with the crimper (which holes to use) I had a quick practice on the 14/0.30 8.75 amp wire. A very professional looking result and I couldn’t pull off the ring terminal even with pliers!
 

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Hi Rusty,

following the instructions which came with the crimper
had a quick practice on the 14/0.30 8.75 amp wire. A very professional looking result and I couldn’t pull off the ring terminal even with pliers!
:thumb I thought I was going to have to explain how to crimp 14-strand wire in 'Lucar-crimp' terminals intended for 28-strand wire, but your lower image shows almost exactly how I do it. The only thing I'd advise against is the strand ends protruding from under the conductor crimp - they'll make it difficult to slide any separate insulator over the terminal after crimping.

Fwiw, another tip. Especially in long wires that also bridge between frame and headlamp shell, I add a little extra wire length before cutting and terminating; doesn't need to be much - one turn around a finger, pencil, etc. Then, after I've used the bike a bit, I check if the loop's been pulled tight; if it has, I just disconnect one end, remove the remaining twist in the wire and reconnect. Reason is, that's :thumb to do than replacing a (especially long) wire that turned out to be a centimetre or so too short/tight after some use. :(

Hth.

Regards,
 

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Discussion Starter #15
With the demise of my battery carrier, its subsequent removal and better access I thought I may as well make a start on the re-wire. First job is to remove the old covering, where the original fabric was still in place this was easy, it was as rotten as a pear and fell off without much effort. The various insulating tape bodges were a different matter and when I did eventually get it off there was a disgusting gooey mess underneath, even on one of my own very recent 'repairs'.

I've only tackled the under seat area so far but I haven't come across any anomalies. The wire colours are correct and I have one errant female spade with two red wires coming from it, one goes to the frame and the other to the rear light. I think this was the original rectifier earth.
 

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Discussion Starter #16
The rear light unit is off and there are no horrors I'm pleased to report. A separate earth wire had been added by the PO from the unit servicing the two indicators and the rear lamp/brake lamp, this went straight to the battery positive terminal but still used the unit as a conductor. I’m hoping to improve this by running dedicated earths from each lamp to a multi-way sleeve connector under the light unit, the one red wire coming out of the connector will then go to the battery positive via the main fuse.

Once I've got the lenses off I'll look at replacing the lamp feed wires as well, I've got some button connectors so should be do-able.
 

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Hi Rusty,

rear light
Interesting for a '72 ... I would've expected an original rear lamp to have its own Red wire threaded beside the Brown and Brown/Green wires, the Red wire ending in a push-in bullet terminal in a loop attached to the outside of the bulb-holder. Aside, all the ones I'd seen had led me to believe the Red wire was standard from '71 but there were several BritBike posts years ago indicating not all '71 bikes had the Red wire into the lamp; it's possible early '71 bikes - more sent to the US - didn't have 'em but later bikes - more remaining in GB - did?

Then the 5-way sleeve connector hidden in the pressed-steel rear lamp and indicators mounting joins Red, Brown and Brown/Green rear lamp wires plus one from each indicator to their corresponding wires from the main harness.

If you're reusing the lamp unit and can't thread a Red wire into it beside the Brown and Brown/Green wires, fwiw I attach the Red wire with a 3/16" ID ring terminal under one of the 2BA nuts on the threaded studs that mount the lamp unit on the pressed-steel bit. Only other thing to check is if the 'frame' between the bulb-holder and mounting studs is one- or two-piece; 'original Lucas' were two-piece and Lucas wrapped the tiniest-ever piece of braid around both for an earth path ... :rolleyes: if the braid hasn't rusted away in the last 47 years, it's easily-lost ...; otoh, a pattern 1-piece 'frame' is obviously better.

dedicated earths from each lamp
lenses off I'll look at replacing the lamp feed wires
Are you planning to run both wires down the stem, or just attach each indicator's earth to a ring terminal under the stem nut inside the pressed-steel mounting? If you want to run both wires down a stem, bear in mind ID aren't always the same :rolleyes: and two 14-strand wires aren't likely to fit; ime two 9/0.30 wires fit sometimes ... :) or the return wire could be uninsulated? Then solder the return wire to a washer that fits in the bottom of the bulb holder - once the spring and bulb are fitted, the washer'll make good contact. :thumb

Hth.

Regards,
 

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The rear light unit is off and there are no horrors I'm pleased to report. A separate earth wire had been added by the PO from the unit servicing the two indicators and the rear lamp/brake lamp, this went straight to the battery positive terminal but still used the unit as a conductor. I’m hoping to improve this by running dedicated earths from each lamp to a multi-way sleeve connector under the light unit, the one red wire coming out of the connector will then go to the battery positive via the main fuse.

Once I've got the lenses off I'll look at replacing the lamp feed wires as well, I've got some button connectors so should be do-able.
Hi Chris,

I did exactly that in restoring my 72 T100R this summer. I was able to feed a red wire down each of the 2 indicator stems (bit tight, but with a thinnish wire it's do-able, ring terminal on the lamp end attached to a self-tapper in the lamp holder) and plumb those into the red earth that connects back to the loom. As Stuart says, my tiny bit of copper braid in the tail lamp was so fragile I bypassed it with another earth wire and so all my rear lights are earthed directly by wires back into the loom. Works perfectly.
 

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Discussion Starter #19
This is what I’ve got having removed some of the lenses. One indicator is a genuine Lucas and will accommodate another 14/0.30 red wire along the stem, the other is fake Lucas and won’t. It’s a bit academic anyway because all of the red wire I bought was 28/0.30 (against Stuart’s advice I might add) and that won’t go down either so I need to go shopping again. I’d like to use the stems to keep the earths internal and out of the weather.

The rear light looks more of a problem. I have a braided copper wire attached to a male spade, I could replace that with a female spade and run the red wire next to the bulb holder and out through the rubber boot but it all looks a bit tight for space. Alternatively, and my favoured option, I could solder a wire to the bulb holder and run that directly out through the boot retaining the braid as backup. I can’t see any 2BA studs.
 

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Hi Rusty,

rear light
can’t see any 2BA studs.
Sorry, it's bolts on yours - through the rear part of the black steel "Tail lamp support" and the rubber lamp backing, screw into the 'frame' that supports the bulb holder and the lens.

I could replace that with a female spade and run the red wire next to the bulb holder and out through the rubber boot but it all looks a bit tight for space. Alternatively, and my favoured option, I could solder a wire to the bulb holder and run that directly out through the boot.
If there's space to run a thin (9/0.30?) Red wire beside the Brown and Brown/Green wires, will a flag terminal fit over the bulb-holder tab the braid's currently attached to? If so, that's what I'd do - flag terminal in place of the braid on the bulb holder, Red wire from it to the connector for the indicators earth wires in "Tail lamp support"? "braid as backup" seems to be just complicating something simple?

use the stems to keep the earths internal
Up to you of course but I've never had any trouble from: disassemble the indicators, clean each thread with a brass wire brush, reassemble with a smear of graphite grease (no chance of it being an insulator) on each male thread, Red wire attached to a ring terminal under the stem nut - on your bike, the ones inside the "Tail lamp support".

Hth.

Regards,
 
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