T100R Re-Wire - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 32 (permalink) Old 09-28-2019, 05:09 PM Thread Starter
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T100R Re-Wire

With Stuartís much appreciated help Iíve 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) Iím starting from scratch and have absolutely nothing in the garage to do this job and b) Iíve made allowances for the inevitable mistakes, Iím in over my depth.

This thread might be useful for others so Iíll update it with progress (and Iím 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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post #2 of 32 (permalink) Old 10-01-2019, 11:52 AM Thread Starter
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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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post #3 of 32 (permalink) Old 10-01-2019, 12:11 PM
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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.

Last edited by CafRacer; 10-01-2019 at 12:22 PM.
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post #4 of 32 (permalink) Old 10-01-2019, 03:02 PM Thread Starter
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Thank you Scottty, very helpful.
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post #5 of 32 (permalink) Old 10-01-2019, 03:33 PM
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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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post #6 of 32 (permalink) Old 10-01-2019, 03:36 PM
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Hi Rusty,

Pleased I could help.

Quote:
Originally Posted by Rusty1 View Post
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 ...

Quote:
Originally Posted by Rusty1 View Post
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.

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?

Quote:
Originally Posted by Rusty1 View Post
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.

Quote:
Originally Posted by Rusty1 View Post
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.

Quote:
Originally Posted by Rusty1 View Post
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.

Quote:
Originally Posted by Rusty1 View Post
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.

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 ...

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,

Stuart
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post #7 of 32 (permalink) Old 10-01-2019, 04:22 PM
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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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post #8 of 32 (permalink) Old 10-01-2019, 04:43 PM Thread Starter
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Quote:
Originally Posted by StuartMac View Post
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 . 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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post #9 of 32 (permalink) Old 10-01-2019, 07:45 PM
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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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post #10 of 32 (permalink) Old 10-02-2019, 04:54 AM
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Hi Jimmy,

Pleased I was able to help. But you were the guy that did the work and got the bike running.

Regards,
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