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#841529 03/01/21 5:09 pm
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mrcarb Offline OP
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Looking for the fuse rating for a 65 Atlas and cannot find it in the repair Manual. Would someone here know the fuse rating?

Thank you in advance.

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20A


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The american fuses rating would be 15A SFE 32V

Head light, horn and brake light should not blow.


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Hi Dave, is that shown in the repair Manual? I am curious as to where you have seen the rating. Thanks

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Are you seeing any fuse in the Manual? I’m not.

A 20 A fuse will work. A 15 A will probably work too.

Best place to put the fuse is in the return lead, close to the battery.


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etheir 15 or 20 amps will work .

the american fuse rating is kind of common britbike knowledge , ( there is a triumph factory Bulletin )
American fuses are sold at there continuous rating ( roughly about half the blow rating )
the Lucas fuses were sold at their blow rating ( roughly twice their continuous rating )
this can leave some confused and fitting fuses way to large
to safeguard the wiring .
[Linked Image from morriesplacecycle.com]

the factory would have fitted a Lucas 35/17 fuse .... with the 17 amp part being
the continuous fuse rating you are trying to match . ... ( 35 is the blow rating )
( these fuses were never that common in the USA )...but if you want to pay to much
for a fuse they are available online ... while the equivalent American fuse is already in every parts store

so to fit todays normal glass fuses you
need to round-down to 14 or 15 amps
or round-up to 20 amps ,.. either will work ... unless you are trying to fit a Lucas glass fuse holder
in which case .... the length of the fuse is as important as its ampacity .

a 14 amp SFE fuse will be short by 3/16" ( which can cause overheating from inadequate spring tension )
a 20 amp SFE fuse will be a good fit ( SFE uses the lenght to also connote ampacity )
a 20 amp AG fuse will be a good fit

there are also "combo"
SFE/AG fuses that are all 1 1/4" long ... either a 15 or 20 amp will work .
these fuses eliminate the length differential associated with SFE fuses


if you fit a modern mini-blade fuseholder with either a 15 or 20 amp fuse
you wont have to remember any of the obscure glass-fuse length minutiae .

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Really I was hoping to see some documentation. I have been using a 20A SFE fuse in my BSA Lightning.

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Its not really rocket science, the fuse is either big enough or its not !!

There has been some discussion in the past about fast blow or slow blow fuses,
this has blurred the numbers about what is actually required, and what you can find in the local auto store.

I'd also question about whether the horn is included in the fused side of things.
Horns can have a very big initial power draw, followed by a fairly low(ish) current.
For this reason they are mostly not wired through the ammeter either.
This can take some figuring out from the wiring diagram.
They seem to obscure this as much as possible ... ?

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Originally Posted by mrcarb
Really I was hoping to see some documentation. I have been using a 20A SFE fuse in my BSA Lightning.

The document I’ve seen is the wiring diagram in the Manual. It shows no fuse.


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That actually raises the question of when did Nortons first actually provide a fuse in the wiring. ?

I know the least reliable part of the wiring in an 850 I had was the fuse fitting.
Until it was replaced, it was not possible to get a reliable connection.
It had done a few miles by then though ...

And if you've ever had the lights go out at night, I'd comment that its much more preferable to have the harness
fuse itself along the way to give you some warning, rather than have the lights just go 'blink' NOTHING !

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Yes, a fuse on a vehicle is an important safety feature. It can stop you being burnt to death in your bed.

So they invent a dangerously unreliable fuse and holder!


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Fuses appeared in wiring harnesses & diagrams around the same time as the change from 6V to 12V. So a 65 is on the cusp of the 6V/12V change hence no fuse in the wiring diagram is not a surprise. If you want documentation then look at the later wiring diagrams.

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John Healy recommends a 20 amp US fuse here https://www.britbike.com/forums/ubbthreads.php/topics/78435 and says the mistaken use of a 35 amp fuse (British rating) will cause a meltdown or fire.

Also, https://britbike.com/forums/ubbthreads.php/topics/663398

Last edited by linker48x; 03/02/21 8:45 pm.
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Originally Posted by linker48x
John Healy recommends a 20 amp US fuse here https://www.britbike.com/forums/ubbthreads.php/topics/78435 and says the mistaken use of a 35 amp fuse (British rating) will cause a meltdown or fire.

Mistaken use of a 35A US rating fuse.

https://www.mgtoronto.com/pdf/Tech/fuses.pdf


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