Diagnose this....

[Oakie]

A couple of weeks ago the headlight fuse in my bike blew. No great worry and easily fixed. It happened again today. This is where it get's interesting.
Instead of replacing the 10amp fuse with a 10 amp, I put a 15amp in it's place. All well and good. The bike started fine, headlight worked again but when I went to try out high beam there was no high beam and the engine cut out. Started it up again (lights on dip) flicked the lights onto full and once again there was no full and the engine cut out. I turned it off then turned the ignition on again but did not start the bike. Lights were fine on dip but when I flicked them onto full, well there was no full beam. I turned the ignition off but when I turned it on again I noticed no idiot lights going. Full check revealed that I now have NO electrics at all. No starter, horn, indicators ... nothing.
I've checked all the fuses and they are intact. Any ideas?

[kwaka750]

Had a similar issue, turned out to be a loose earth, might be barking up the right tree, but worth checking. Unfortunately buy the time I found out it was a loose earth had melted half of the earth wire and had to replace it, and only started checking after my entire dash went ou lol. Definitely learnt from that one, but I digress, I would start by checking earths.

[JimO]

you may find there was a 10 amp fuse for a reason

[Oakie]

you may find there was a 10 amp fuse for a reason

Yes, I remember that from my high school physics but as there was a 30 amp fuse sitting in the 'spare' fuse holder I hoped I might be able to get away with the 15amp replacement.

[idb]

I'd remove the headlight high beam fuse altogether and start again.
Check your connections at the battery, if a fault has been dragging a high current through the battery terminals they could have developed a high resistance.
Remove them and clean them up.
Now see if everything else is working (still with the headlight fuse out).
If so, the fault is in the high beam circuit, just work your way through it from the fuse.

[Oakie]

I'd remove the headlight high beam fuse altogether and start again.
Check your connections at the battery, if a fault has been dragging a high current through the battery terminals they could have developed a high resistance.
Remove them and clean them up.
Now see if everything else is working (still with the headlight fuse out).
If so, the fault is in the high beam circuit, just work your way through it from the fuse.

I see the logic in that. However I have done as you suggest and still no electrickery anywhere.
I guess though that it may prove that the problem is not in the high beam circuit?

[idb]

I see the logic in that. However I have done as you suggest and still no electrickery anywhere.
I guess though that it may prove that the problem is not in the high beam circuit?

Do you have some sort of voltage detector?

[Spuds1234]

Had a similar problem. The bike wouldnt start using the starter motor.

All the lights would work on the dash etc, but when I hit the start button it would just click.

Sometimes the dash lights would go out. Fuse was still good though.

Turned out to be a loose earth connection at the battery. A good enough connection to run the lights and shit, but not the starter motor.

Strip your bike down and starting at the front of your bike, check every wire and connection and make sure its all good.

Also try charging your battery.

[James Deuce]

Barring a loose earth wire, it's a Honda (not being facetious here) so start diagnosing with a multimeter at the output end of the regulator/rectifier.

[Drew]

Does it have a fairing? This happens on gixxers a lot, and the fault is often a pinched wire, shorting out on something. If no fairing, check in the headlight for something similar. It is most likely a short in the headlight circuit, so shouldn't take long to trace back.

[Oakie]

:slap: :slap: Well I have at least got my bike mobile again now. On the premise 'when all else fails, read the instructions' I sat down in front of the CB400 manual that Inline4 sent me ages ago and opened the page about fuses. There I spied the fuse box that I'd checked all fuses and replaced the blown one. Immediately below that though it showed "...the main fuse located on the starter magnetic switch". Doh. I didn't think that all of the fuses wouldn't be in the same place. Anyhoo. I found the switch, took the connector off to free up the fuse and lo and behold, it was indeed blown. Replaced it and everything goes again although I still have the original problem of the high beam flicking off a second after I turn it on.
So I guess the train of events was:
> there is a short circuit or something in the high beam circuit
> eventually this blew the original 10amp fuse and killed the headlight circuit
> replacing the 10amp headlight circuit fuse with a 15amp has caused the main fuse to blow

I've gone back to a 10amp fuse in the headlight circuit and just won't use high beam until I get it fixed.

Thanks for your advice everyone. It's good to know there's quick advice out there when I need it. Cheers!