SOHC.co.uk Forums > CB500/550

Loom and part i have labelled but ink faded

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MikeM:
that's coming out of fusebox hence concerned


bad earth still  ?

Lobo:
Mike - guess you realise you've a fairly big issue here, and from the pics it'd seem your whole earthing system needs renewing. There appears to be so much damage that its a fair bet there's more you can't see.... certainly a replacement 'green' wire through the whole bike appears needed, if not a loom.

What's caused this? Two possibilities come to mind...

(1) the previous owner installed excessive lighting / electrical loads and replaced the Honda rated fuses with higher amperage ones.

.... or, and more likely...

(2) the bike's multiple earthing points were poor / in disrepair.

Up & down the bike there are individual circuits.... denoted & protected by the fuses. Each circuit has its own current rating... eg 15A, 5A... and so on..... and yet they all share the common Earth wire; which is rated @ 15A.

Now, and for arguments sake, if this green (15A) wire was earthed only at the rear mudguard current from the headlamp, indicators, horn, stop, tail, ignition coils, alternator exciter coils etc etc would all be 'sharing' the wire / connection & very quickly it'd overload & melt. (= yours?) If however all the earthing points were good, the front end of the bike's current will earth into the frame @ coils area, the mid bike current around the battery box area, and the rear end into the rear frame earthing point. IE a 'concentration' of current would never be allowed to build over the length the wire.
Very, very over simplistic, I know, but hopefully an illustration. (think of a busy motorway with all slip roads blocked.. it'll soon overload as traffic can't bleed off of it)

The integrity of your earthing wire is very much in doubt, and a repairing of the visible damage will still leave the invisible bits waiting to fail. Bad news, but whilst you've the bike in bits now is the time to fettle it. Other folk may have different views, but given the loom may be 35 years old with brittle insulation, fatigued wires about the steering head, dirty connectors etc maybe just bite the bullet & order a replacement loom for peace of mind. Failing this, run a new green earth wire to all user points in parallel to the old / burned out wire.

Crappy, I know. See what others have to say, hopefully there may be a better way forward.
Simon

MikeM:
hi

thanks for info, time to stop and think.

It appears the green wire damage goes to the coil?

fusebox green wire again looks hot shall we say.........

so I have another spare loom but not sure how good that one is will have to open it up.

if I have to use new loom looks like I will have to wire up clocks which I am concerned is beyond me

will await more opinions  :)

Trigger:
Mike, mine was the same. I got hold of a new fuse box and replaced all the earth wire. It is weird because mine looked identical to what you are showing in your pictures.

MikeM:
did you take any pics.... how does/did buying a new fusebox solve the issue ?

want to learn about electrics

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