Cb550f blowing main fuse

[Oddjob]

It's a bad bodge then, you risk a fire doing that.

[Otis]

30amp is way too high. 15 is more like it.

Thank you for confirming as I only replaced the first one with what was already in there. Even the Haynes manual doesn't appear to give guidance on fuse ratings but that doesn't surprise me. In the last 50 years I have never found a Haynes Manual to be useful: it only gets you into deeper trouble because it gives the impression it is thorough but they are pretty much all useless.

Maybe that was a bodge by the previous owner because it was blowing 15A fuses?

That sounds very likely because there have been a couple of iffy things that I discovered.

[Bryanj]

I think you need to start from scratch with an ampmeter that can handle 30ish amps put in circuit DO NOT USE THE STARTER!!!!

Dissconnect everything then start carefully reconnecting and wiggling(technical term!) all the wiring and connectors to see if you can get a high current draw.

Primary suspects from years of problems are :-

Idiot light bulb holders
Wiring under seat
Indicator wires through stems
Rats nest in headlamp
Wires through the bars

[Otis]

That's useful information, thank you.

OK, so I have done as you suggest and replaced the fuse again and turned everything off. The battery is reading 13.3V.

Ignition on - no problem
Headlight on both dip and full - no problem
Horn - no problem
LHS indicators - performing as expected
RHS indicator front bulb just stays on and doesn't wink and the RHS rear bulb does not light up at all. I swapped bulbs and it isn't the bulb so first area of suspicion!
Front brake lever operates the stop light with no problem but footbrake does not operate the brake light so second area of suspicion!
Kick started the bike and she runs as expected but the two identified areas of suspicion remain the same.
During these checks nothing appeared to blow the fuse again which is perhaps disappointing.

If any of the above suggests anything to anyone and can possibly narrow down the areas to attend to next it would be really appreciated.
 

[Bryanj]

Both those items have wiring under seat.
Rear brake light switch first connectors are in the rubber boot where yellow and blue wires from points join into loom, bulb should light if black and green/yellow joined, if yes new switch if not wiring.
Indicator will be either light blue or orange and connect in big rubber boot under seat near to seat support accross frame, first use a seperat earth wire from ind body to batt neg, wouldnt be first time a slightly loose mounting stopped on working!

[Otis]

Thanks Bryan,

Since my last post I have now discovered that the winker relay is shot so new one is ordered. I also traced the wire from the rear brake switch and found a black wire completely severed. As it is impossible to get at I am now in the process of removing the complete air box and all associated paraphernalia. What a nightmare to get at.

Whether either or both of these were the cause of my blown fuses remains to be seen but it's always nice when you do actually find a fault.

[Bryanj]

If the black from the loom touched anything metal that would blow your fuse as black wires are 12v positive when key is turned on

[Otis]

If the black from the loom touched anything metal that would blow your fuse as black wires are 12v positive when key is turned on

The offending black wire that almost certainly has to be the culprit.

Just as an aside, I purchased a repro winker relay from David Silver for £18.50 delivered whereas they wanted £51.50 for a genuine part, the differential being just too far apart.

[Towsejames]

I have around 3-4 full clutches for the 550. You want a set of plates, steel or friction?

Just pay the postage.

Very interesting! I’ll send you a message


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[Bryanj]

That wire definately looks like its rubbed through on something

[TrickyMicky]

If the black from the loom touched anything metal that would blow your fuse as black wires are 12v positive when key is turned on

The offending black wire that almost certainly has to be the culprit.

Just as an aside, I purchased a repro winker relay from David Silver for £18.50 delivered whereas they wanted £51.50 for a genuine part, the differential being just too far apart.

For what it's worth, I have fitted the (hopefully!) attached digital flasher unit to both my 400 and GB250. It will operate with either filament or LED bulbs, or even a mix of the two, the flash rate remains the same. Like yourself, the initial reason for this being an original OE flasher for the GB250 was only available from Japan at £112 plus carriage.  The only downside I have found so far being if a bulb fails, the unit just carries on regarldless at the same flash rate. I found that it fitted into the rubber mount on the 400 quite qell.

[Otis]

OK, I am now completely stumped.

With the help of you fantastic guys I have rectified all of the problems I had. I found a broken black wire from my footbrake cable and repaired it. I discovered a problem with my indicator flasher unit so ordered a new one which arrived today. I replaced my 30 amp main fuse with a 15 Amp as per your good advice. I put everything back together and before installing the new flasher unit I ran a check. Apart from the RHS flasher not working everything was as expected. Whilst she was idling nicely, I disconnected the old flasher unit and installed the new one only to find that the bike immediately stalled.
I realised straight away that something had gone but found that the fuse was still intact. I now have absolutely no idea what I have caused but the fuse is fine but there is absolutely no life whatsoever in anything although the battery is still reading 13 Volts.

Any thoughts please because if it's not the fuse then I haven't got a clue what to do.

[Bryanj]

Check the voltage both sides of the fuse then at red wire of switch when turned off then black wire of switch tirned on.
What you are doing is checking for 12v at every junction point from battery onwards, wouldnt be first time a wire got accidentaly unplugged or a damaged wire, or switch, coincidentaly gave up

[Otis]

Check the voltage both sides of the fuse then at red wire of switch when turned off then black wire of switch tirned on.
What you are doing is checking for 12v at every junction point from battery onwards, wouldnt be first time a wire got accidentaly unplugged or a damaged wire, or switch, coincidentaly gave up

Bryan, you are a gem my friend. Whilst I hadn't intentionally separated some connectors when I moved the assembly I must have inadvertently separated a connector which I have just discovered and all is now well.

I owe an awful lot of you guys a pint each for the help you give. Thank you

[Bryanj]

People are frightened by electrics but if you are methodical its actually easy, long distance diagnosis is not very easy and i find if i give precise instructions on testinga lot of people disapear off on a tangentand i am afraid at this point i tend to give up and go quiet, you are at least listening!!!