Blown main fuse

Here you can talk about all kind of TECH for the B50 B44 B25 And Other BSA unit Singles

Moderator: minetymenace

Post Reply
JerryT
>60
>60
Posts: 67
Joined: Wed Oct 30, 2019 8:51 pm
Location: BARNSLEY

Blown main fuse

Post by JerryT »

The main fuse on my B50T blew on the M1 earlier today.
I had travelled about 20 miles at this point.
A friend picked my up with the bike in the back of his van and as soon as I got back home I put in a new fuse and the bike fired up first kick.
Electrics is definitely not my strong suit.
Can anyone point me in the direction of a likely fault.
I am running the specified 35 amp fuse.
Thanks
Jerry
User avatar
JB
>480
>480
Posts: 499
Joined: Tue Jun 15, 2004 8:32 am
Location: Devon, England

Re: Blown main fuse

Post by JB »

Sorry to hear that Jerry.

It's possible the fuse could have gone for physical reasons and that's why glass fuses are useful, you will be able to see if the fuse has either melted (electrical) or simply broken.
If it's failed due to a short circuit then it's not always easy to find the reason why it failed, although most often a visual examination will locate the cause and a meter will help to confirm it, old bike electrics are pretty basic... it's not normally too hard finding the cause.
It's always worth carrying a spare fuse as every spare fuse at least gives you a chance to resolve the issue.

Edit: Out of interest have you checked the fuse was blown? The reason I ask is that the ignition switch on these models is notorious for playing up and losing contact, giving the appearance that the fuse has gone, often just turning the key on and off will regain contact.
JerryT
>60
>60
Posts: 67
Joined: Wed Oct 30, 2019 8:51 pm
Location: BARNSLEY

Re: Blown main fuse

Post by JerryT »

Thanks for the reply JB.
The first thing that I did was remove the side panel and checked the ignition switch for a detached cable. (My switch is mounted on the side panel)
The switch seemed to be fine so secondly I checked the fuse and found it to have blown.
I suspected the electrical system as the engine cut cleanly with no spluttering or sound of mechanical failure.
Jerry
BSA_WM20
>900
>900
Posts: 924
Joined: Sun Dec 24, 2006 2:09 am
Location: Sydney Australia

Re: Blown main fuse

Post by BSA_WM20 »

I had this happen regularly on my B 50 T
Seemed to be quite random .
Ended up being the steel side cover having cut through the gromets managed to touch the neg terminal on the battery and poof, no more fuse .
Took a long while to find it.

The A 65 L had one of those idiot in line stop switches on the front brake
It also shorted out on the inner and that took an even longer time to track down as it only happened when the brakes were pulled on very hard.
Bike Beesa
Trevor
User avatar
minetymenace
Gerry1
Gerry1
Posts: 7731
Joined: Wed May 26, 2004 1:00 am
Location: On the edge of Salisbury Plain, England
Contact:

Re: Blown main fuse

Post by minetymenace »

Intermittent faults are hard to find, if it is a solid fault, arm yourself with a box full of 2A fuses and start pulling the loom apart until the fuse doesn't blow. Most likely to be something rubbed through or the mass of connectors between the electrics box and the bars...

I rewire all my bike as a new loom will probably last me out, but I am embarrassed to say that the <12fs is currently languishing with a blown fuse!!
There is no evidence to support the notion that life is serious.
Abyssinian Wire-Haired Tripehounds Gnash.
Post Reply