cb 250n superdream blowing fuses

biker_king · Renault 5 Driver Joined: 28 Jun 2007 Karma :

hi i have been re building a 1980 cb 250n which i will post picture of when im finished,
the problem is it keeps blowing the main fuse whenever i turn the ignition key on, the battery is reading
11.98 volts and the bike has not been run for about a week.
first i fitted a 15amp fuse and then a 20 amp and it still burnt it?

any ideas would be great thanks.

biker_king · Renault 5 Driver Joined: 28 Jun 2007 Karma :

ok i still have the same problem and have spent some time going over all the erth connections ect and their all good, would a faulty diode cors the problem as my one has no continuity in ether direction?
is there anything els that would corse my fuses to blow instantly.
any help would be useful at the moment , thanks.

also i put the battery in both my other bikes and it seems fine so the battery is ok.

NSR Mick · World Chat Champion Joined: 26 Jun 2005 Karma :

A battery alone wont blow fuses. A direct short to earth will.

Is everything turned of when you turn the key? lights and indicators etc..
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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

You have a short circuit. Stop replacing fuses and go find it.

You might find some of the wire is a bit melty or scorched near the guilty party.

Pay particular attention to where the wiring runs past the headstock for any frayed/worn/broken wires. Also check no wires are trapped under bodywork.

Also make sure no wiring has dropped down onto any hot engine parts and melted through. Basically, check anywhere a live wire can touch the frame.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

mh · L Plate Warrior Joined: 05 Mar 2008 Karma :

I had the same problem a while ago (see https://www.bikechatforums.com/viewtopic.php?p=1741558 ).

In the end, £7.50's worth of replacement loom sorted it out (try eBay, or a breaker). Seemed easier than trying to chase broken wires in a 27 year old loom...

Good luck!