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Originally Posted by Stuart
Afaik, the closest to 17.5A rating you might find on non-electric-start Commandos are 28-strand wires to the battery terminals?

The battery brown/blue and red terminal wires were also 14/32 but with double (or some have triple) positive (red) wires to the battery ring terminal.

https://andover-Norton.co.uk/en/shop-details/17462

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Thanks to all for the great data points.
I'm going to jump from the Pazon feed to the front brake switch but add a 7.5A blade fuse in a weatherproof housing between connector and Pazon box.
The brake switches are new as well as the harness, so hopefully that will kick any corrosion issues far enough down the road to be moot. To me anyway.


1970 T120R - 'Anton'
1970 Commando - 'Bruno'
1967 T120R - 'Caesar'
1968 Lightning - 'Dora'
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Hi Les,
Originally Posted by L.A.B.
The battery brown/blue
terminal wires were also 14/32
https://andover-Norton.co.uk/en/shop-details/17462
That says "1971-74". I'd expect 14-strand '71-on but did Norton have that originally pre-'71? Ime, Triumph and BSA had 28-strand (I was surprised only the first pre-'71 Triumph I worked on).

Regards,

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Originally Posted by Stuart
Originally Posted by L.A.B.
The battery brown/blue terminal wires were also 14/32
https://andover-Norton.co.uk/en/shop-details/17462
That says "1971-74". I'd expect 14-strand '71-on but did Norton have that originally pre-'71? Ime, Triumph and BSA had 28-strand (I was surprised only the first pre-'71 Triumph I worked on).

I only chose that as an example because it shows the battery terminal wires (I wish vendors, not just AN, wouldn't show pictures of harnesses tightly coiled up) but I don't think the '68 or 69-70 harness battery wires are any different to '71-74 and the 850 Mk3 isn't although like the T160 it had the dangerous harness positive battery terminal that shouldn't be connected.
My T140 and T160 don't have any heavier battery wires.

The front brake switch wiring was an addition to the original Commando harness apparently due to a US requirement to have a switch for each brake from '69 and the brake cable with switch was "USA only" at that time and it seems they saved a few inches of white wire by powering the front brake switch from the ignition feed to the coils and not as shown on the GTiller diagram. The pre-71 factory diagram (the only one I know of) doesn't show the front brake switch wiring.

Edit: Factory diagram.
[Linked Image from i.postimg.cc]

Last edited by L.A.B.; 07/24/21 8:02 am. Reason: Wiring diagram
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Originally Posted by L.A.B.
...The pre-71 factory diagram (the only one I know of) doesn't show the front brake switch wiring.
I have that same diagram, hence my confusion about where to intercept power.


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Here is the 1970 BSA A65 where the front brake switch was fitted to both US and non US bikes.

[Linked Image from i.postimg.cc]

That shows the rear brake feed to both brake switches coming from the coil white wire connection. So that was one of Lucas's solutions at the time.

For the 69/70 B44/B25 they instead took the feed for the rear brake switch from the ignition switch(as previous years) and the front brake switch from the coil. So a second solution.

[Linked Image from i.postimg.cc]

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.
Originally Posted by Stuart
Quinten, Quinten ... facepalm

You've been posting about electrics on this Forum for years and years ... Sometimes I believe you've finally begun to grasp some of the basics, then you burst my bubble posting things like:-

Originally Posted by quinten
the white wire in a normal harness is rated to 20 amps ,and fused at 20 amps ( 17.5amps in old money )
facepalm Cobblers ... the original single fuse might be 17.5A continuous but there isn't any way on God's green earth any of the wires are rated for that ... Have you really never, ever bothered to look up Lucas wire current ratings or their modern equivalents? shocked

Original 1970 Commando coils and brake switch/lamp wires were 14 strands, Lucas rated for 7.5A

Afaik, the closest to 17.5A rating you might find on non-electric-start Commandos are 28-strand wires to the battery terminals? Originally rated by Lucas for 15A ...

Originally Posted by quinten
comiing through the ign. switch , which may have its own current limitations . (15 amps )
laughing Please do feel free actually to demonstrate 15A though the standard Lucas ignition switch ...

Regards,


Golly whiz stuart , I wasn't aware I needed to meet your approval .
do you have some special expertise ? are you a moderator , i dont think so .
I'm not a bit surprised at this personal attack
Youve been slipping back into your old ways of late
you know
the one that previously got a new banded from britbike

you do not understand the fundamentals of a wire gauge capacity .
they are not found on a simple chart , where the ampacity is de-rated for the less informed .

the resistance of a wire run is it's cross sectional area ... and its length .

Short pieces of any gauge wire can handle higher currents ... than the same cross section in a longer length .
the loads have to be calculated taking into account the length of the wire
and not an amp. number from a generic chart .

Lucas was sizing harness wires towards a maximum ampacity ,
in consideration of the short lengths of the wire runs .
a penny saved was a penny earned .
They knew what they were doing when they sized the wires .
Providing just enough wire gauge to do the job ( at an acceptable voltage loss )
They would have had their slide rules out and double-checking what they could get away with .
( nowadays there are online voltage drop calculator )

you dont fuse a wire at 17.5 amps unless It can do the job
Otherwise there's no point to adding the fuse at all .
( in fact every point in the harness must hold upwards of 40 amps... for the 1/10 for second a total short will draw )
During this time the wire loss will climb to 10 ~15 %

You can pull 20 amps through 3ft of 14 awg gauge wire at 14 volts
with acceptable voltage drop under 3%

14 ga ...voltage drop of 0.37 volts or 2.66 % loss

16 ga ... voltage drop of 0.48 V or 3.44% loss

18 ga ... voltage drop is 0.77 V or 5.47% loss

You and I probably wouldn't build a custom harness with these losses
but Lucas would .

( I'll let someone else figure out converting awg to swg ) ... or counting the strands and diameter .

my statment stands as written , a stock harness will pull those loads ,
It may have to ... if a 20 amp fuse is fitted and blows .

Last edited by quinten; 07/24/21 5:31 pm.
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Just seen the above, can't believe it's still untouched ... shocked

Originally Posted by quinten
my statment stands as written
Your "statment" (sic) is still completely, totally, utterly wrong.

In constructing the above and your previous post, the bit you've missed (at least I hope you just didn't know it, one would hate to think you ignored inconvenient facts to 'prove' a point ...) is Lucas was using "14/32" wire lo-on-ng before they ever fitted any fuse to any motorcycle harness.

Originally Posted by quinten
20 amp fuse
You have development events in the wrong chronological order and have extrapolated from the wrong one:-

. Lucas never fitted a 20A continuous fuse to any motorcycle harness it supplied to North America. The fuse you have experienced is likely a Littelfuse supplied by North American-based British motorcycle importers to their dealers to save importing the late fuse Lucas fitted, rated 17.5A continuous.

. The earlier fuse Lucas first supplied/fitted (as models/versions (earliest I know of is '64 Triumph 6T Thunderbird) and/or makers converted to 12V?) was only rated 12.5A continuous/25A blow.

. The only reason Lucas uprated from 12.5A to 17.5A was expediency - as more electrical gadgets were added, 12.5A could be exceeded relatively easily, bringing a bike to an immediate halt when it blew; thumbsdown there wasn't (still isn't) a fuse of that type between 12.5A and 17.5A continuous.

Originally Posted by quinten
a stock harness will pull those loads
Made of Lucas 14/32 wire, I know for a fact they won't, at least not for any sensible length of time.

With advance apologies to most readers here, it's unlikely any Norton owner who hasn't ever owned a triple, with Lucas Rita EI switching three '12V' coils, would encounter 14/32's wire's actual current capacity limit. Given you don't have any experience of triples, never mind the other two, you couldn't possibly have any first-hand experience to counteract your theorising in your posts.

The only other possible way another non-triple-owning Norton owner might have encountered 14/32 wire's actual current capacity is a Commando with a RM21 alternator run continuously at 6,000 rpm-plus for probably at least twenty minutes (any takers? wink ).

To be clear, reason I stress "might" in the previous sentence is, while Lucas rated the RM21 for 10.5A @ 5,000 rpm - which 14/32 can just about take without showing distress - I've seen some Commando publicity stating "11A @ 6,000 rpm". My first-hand experience - of a couple of triple short-circuit racers using Rita with three 12V coils - is 14/32 then shows distress inside twenty minutes ... I've previously posted the joke, "Brown/Blue turns brown/crispy" ...

This Board's moderator being "Dynodave", given his experience with Rita EI, his attention drawn to "Rita EI switching three '12V' coils" might remind him of his own first-hand experience; hopefully then some correction finally might be applied to the tosh in your posts ...

Originally Posted by quinten
you do not understand the fundamentals of a wire gauge capacity
Wrong again. But it's irrelevant. You have simply extrapolated your theories from the wrong reality.

Originally Posted by quinten
You can pull 20 amps through
14 awg gauge wire
Well, yes, but what has that got to do with anything here?

The "14" in "14/32" is the number of strands, it's the "32" that's the gauge - SWG ((British) Standard Wire Gauge) - equivalent to between 29AWG and 30AWG. The total conductor cross-section area is about the same as 19AWG ...

Otoh, 14AWG has a cross-section area a gnat's over 2 mm2, it's bigger than "28/32" that Lucas rated for 15A; Europe rates modern 2 mm2 stranded for 25A inside 'thinwall' insulation and 17.5A inside 'normal' PVC.

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Pitchforks at 20 paces - love it !!

I'd comment that I've just bought an Anderson plug, rated at 50A.
For a small 20A solar system.
If bike wiring was this heavy, they'd weight more, considerably more !

Thats my only contribution to this bunfight ...

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