SOHC.co.uk Forums > CB500/550

Fuse box woes

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bruxby-clive:
I think you should also check the loom over as it is probably corrosion or old wiring that has caused resistance within the cables and generated heat at the weakest point, causing the fuse holder to melt.

deltarider:

--- Quote from: bruxby-clive on July 29, 2022, 10:24:58 AM ---I think you should also check the loom over as it is probably corrosion or old wiring that has caused resistance within the cables and generated heat at the weakest point, causing the fuse holder to melt.

--- End quote ---
This ^ is repeated over and over again. After 46 years, I still don't have indication I have to check the loom and/or its connectors in total. I've had two issues: fuses and their clamps, which can be easily fixed and the IGN KEY switch which needed replacement. As far as the CB500/550 these seem to be the usual suspects.
Often overlooked: the NEG route, where the GREEN wiring is bolted to the frame.
Before disconnecting all connectors in the blind (the US method), which is very time consuming and brings the risk of ruining perfectly good connections, I'd rather do a proper diagnosis via a simple V4 drop measurement. It tells you where to look.

SteveW:
Check the outside of the loom for shiny areas / odd lines in the wrap as in the attached pic.
This is caused by a poor battery negative connection to the frame so the current uses the smaller green earth wires instead.
The green wires get very hot and melt into the other wires in the loom and also cause the tell tale shiny spots on the loom.
The pic is my loom.

SteveW:
This was inside  :o

alexdecker:
Thank you for the responses. I have got it all to work now, with the exception of two (important) things.

I have no spark in 1 and 4. And my hi beam is not working. I have the 550F2 with Off, P, On on the RH switch, and then Lo and Hi on the LH switch.

When I go to Hi Beam, the headlight shuts off. And after a while, it clips the first fuse (the tail one). It is the original Honda headlight.

I also don’t have spark in 1 and 4. I have power at the coils, at B/Y coming out of the coils and at B/Y at the points plate (tested by disconnecting them from the plate and measuring). I have also tested all the spark plugs, and they are all giving blue sparks. Just only in 2 and 3.

Any ideas?

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