Britbike forum Forums British Motorcycle specific Brands Norton bulletin board 1970 Commando front brake switch power

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

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.

Hi Les,
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,

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.

I have that same diagram, hence my confusion about where to intercept power.

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



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.

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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 .

Just seen the above, can't believe it's still untouched ...

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.

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; there wasn't (still isn't) a fuse of that type between 12.5A and 17.5A continuous.

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? ).

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 ...

Wrong again. But it's irrelevant. You have simply extrapolated your theories from the wrong reality.

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.

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 ...