cb500 dead short

[McCabe-Thiele (Ted)]

Firstly I am assuming that you did not disconnect the battery over winter & that as you describe it the bike was fine last year - nothing has changed as the bike has just stood unused - it just started to blow fuses when you turned the ignition on after the winter rest.

I'm racking my brains as to what could deteriorate as it has stood over the winter - it seems unlikely that a wire could chafe or that an alternator wire would somehow become disconnected and short as it has stood.

My only ever experiences of a similar type of problem was when a rectifier had rusted causing a short in the casing & when a regulator stuck - two separate episodes first one on a bike, the second on a car.

My suspicion is that if such a failure has blown a number of fuses it is likely that wiring in the loom has overheated leading to further dead short. I mention this as if something has caused the loom to fail replacing the loom could lead to another loom failure.

Not sure if it is possible that major internal  battery cell failure could be a cause?
Might be worth checking the state/condition of the battery.

[RGP750]

Thanks for your thoughts. Battery off over winter on optimiser.
Motobatt , seems fine.
I took the loom off last night and externally looks fine I assume I have to unwrap it to check every wire.
That's the bit I can't get my head around , it was running fine

[paul G]

Why unwrap it just use a multimeter and the wiring diagram.

[Toko_Jo]

Thanks for your thoughts. Battery off over winter on optimiser.
Motobatt , seems fine.
I took the loom off last night and externally looks fine I assume I have to unwrap it to check every wire.
That's the bit I can't get my head around , it was running fine

Like I said in my previous reply,  do a continuity check between any black wires and green. When you do that flex the loom at the same time with the meter still connected to see if there is continuity at anytime.

Failing that, you could sent it to that nice chap Ash on here..pretty sure he could check it out...sure he wouldn't mind 

[Bryanj]

Mottobbattt, you didntt by chance fit it backwards, i ask as i know the labeling is not the best

[McCabe-Thiele (Ted)]

Don't want to insult your skills but a few basics to check.
Normally the right hand side of the battery is the Negative terminal when fitted to the bike.
An earth lead goes from this Negative terminal to the engine.
The left side as you look at the battery is Positive and has a connection for the live side.

The battery on my 400 was  fitted back to front when I bought the bike so both terminals were close to the frame. The earth lead had been attached to the rectifier mounting bolt.

My apologies in advance I do not want to offend anyone reading this post. I did wonder if any additional wires had been connected to the live side that might have been left off and caused a short circuit. My bike has an additional permanent fused cable on the live side connected to a special charging plug for my C-tek unit and to a volt meter I have fitted.
Just thinking of any possible reason why all that has changed is you have had the battery out over the winter and now it's faulting.

[taysidedragon]

Have you looked for any evidence of mice chewing a wire or 2? They are notorious for nesting in bikes over winter.

[RGP750]

Thanks Toko Jo I know Ash , I'll give him a call.
As for other suggestions. Yes battery is the right way around
The plug it in and one at a time theory is great if the fuse doesn't blow but as its still blowing it won't find it.
Still head scratching cheers

[Oddjob]

If nothing is connected Rich except for the ignition switch (and you've tested that by isolating it) and the fuse is still blowing then it has to be a short in the loom. When I say nothing, I mean nothing at all anywhere on the bike, rear lights, points, coils etc.

In which case as Jo says, a simple test between black and green should show if it is the loom.

[RGP750]

That's tomorrow's plan. I just hope it shows up.7

[robvangulik]

Thanks Toko Jo I know Ash , I'll give him a call.
As for other suggestions. Yes battery is the right way around
The plug it in and one at a time theory is great if the fuse doesn't blow but as its still blowing it won't find it.
Still head scratching cheers

Replacing the fuse with a lightbulb makes fault finding much easier (and cheaper, doesn't cost so many fuses.)

[McCabe-Thiele (Ted)]

I am baffled as to how the fault has developed Rich - I for one will be very interested as to the cause of problem when you identify it. Iirc it was a new loom as well.🤔

[K2-K6]

I am baffled as to how the fault has developed Rich - I for one will be very interested as to the cause of problem when you identify it. Iirc it was a new loom as well.🤔

All wiring is capacity, doesn't melt under designed for load. And insulation, to prevent leaking into something else.  Well that's the simplified way I look at it.

So, either overloaded with excess or too small to handle the task reasonably. Or, damaged physically, the insulation,  to be insufficient in stopping leaking to give overload.

Checking any multi plugs first to make sure there's no obvious breach to catch you out is worthwhile.

[Oddjob]

I noticed Nigel that the 550F sub loom I bought to replace my old one used thinner red wire from the starter solenoid down the the multi blade connector than the original Honda one, that wire on the Honda one is slightly thicker than the rest, due no doubt to the fact it carries the entire load of the bike, the replacement used the same gauge of wire as the rest. Not a good idea. I intend to replace that wire even though it's brand new. 

[K2-K6]

Some considerable number of years ago I looked at a Ford car for someone with some curios problems.

The throttle cable and clutch cable had both melted their outside plastic covers ! Slow and difficult starting too, he'd left the earth strap off to the engine block after working on it, using starter had then tracked down those two routes in scavenging earth supply to crank it 

Damned leaky stuff yer electrick-tricity  it'll get out with any slight chance offered.