Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: MrBaklava on January 14, 2025, 01:59:21 PM
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Hey folks,
Having a little problem with my 78 CB550...
Yesterday when I turned the ignition key on, no lights illuminated, until I flicked the key off and on again. Today i can't get the ignition to come on at all.
I popped the plug from the back of the ignition and bridged the wires to bypass the switch and there were no changes - the bike is still playing dead.
All battery connections look clean and free from corrosion, and I can't see any blown fuses.
Any ideas?
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If you have eliminated the ignition switch I would check the fuse box itself. My replacement unit from DS was fautly when new,the fuse was good but no power on either end of the fuse holder.
I did a home repair with the soldering iron.
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Just checked and the bike does fire when the starter solenoid is bridged.
If it is the ignition at the key side, can it be removed and repaired or must it be replaced?
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At one time you could buy just the bottom plastic connection part but might be difficult to find now, Emgo did a pattern one BUT there are two types that do not interchange.
It is possible with care to dissasemble and clean the contacts, no johnny five!
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I would use a multi meter to check if there is battery voltage either side of the fuses.....
Or to make sure there is voltage getting thru to the ignition switch. Maybe red wire in, black wire out.
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For the bike to fire (I do assume you mean ‘fire’ and not simply ‘turn over’) there must be some contacts working in the ignition switch in order to feed the coils/ignition. This would also suggest that supply to the ignition is healthy too. Did you mean ‘fire and run’ or simply turn over?
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If you did mean ‘turn over’ and not ‘fire’ I’d suspect the fuse holder unit. I’ve had two fail in exactly the way you have described. Use a volt meter to check continuity from the fuse box feed (red wire from top of solenoid unit) to the outgoing red cable to ignition switch.
Connections in the fuse unit can become very sketchy over time, but can be easily re-soldered. Try fixing before replacing as OEM is prohibitively expensive and pattern ones are not very good quality.
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Thanks for your responses everyone.
I traced a fault to the lower section of the ignition switch (white plastic section) as mentioned by Brianj.
Does anyone know where I can pick up a new one? ideally just the plastic so I can retain my original keys.
Also the bike is a 79 CB550k with the steering lock on the headtube rather than on the ignition.
Thanks again to all that helped out!
[attach=1]
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Try Kojaycat if you are talking about the block connector.
Sorry could not see the photo on my phone, is it broken or does it just need the contacts cleaning up, Cilit Bang Limescale remover is good for cleaning contacts.
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Like Ted said. It’s worth taking the back off (cover with a cloth as the small springs can jump out). Clean with contact cleaner and abrade with wire wool or 400 grade emery and you will be good to go? It’s highly unusual for the triangulated copper contacts to break.
Only risk is that the plastic retaining tags may be brittle, so warm the unit first with a hair dryer.
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There is no such thing as a 1979 CB 550K in fact in UK there is not even a 78 model only 77 which could have been registered late due to poor sales.
You can not get from Honda just the bottom part and a lock set, or even just a genuine ignition switch are both megabucks.
You can get a complete pattern switch for about £50.
As i said Emgo used to sell just the electrical part but you would need to find a supplier, in the 70's there were lots but not now
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I am bored at work so two screenshots for you, no idea if you can get in UK or can get shipped from US
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I’d try dismantling the original and cleaning the contacts first.
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A little off topic: if you want to inspect/clean the killswitch contacts, how do you open it? Can you remove the red cap without breaking it?
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Open up the handle bar switch by undoing the 2 screws. From the inside you can access the contacts. Probably have to loosen up the cable lock nuts as one interferes with the screw removal.
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Thanks. Last year I did a measurement, both voltage drop and Ohms. Nothing is the matter, but it's good to know how to do it. I've wondered, because I've seen quite some bikes with damaged red caps.
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https://www.ebay.co.uk/itm/335596717608
I'm with Phil on this one, open it up and clean the contacts, I've done it before and it's fairly easy.
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I've seen suggestions on this forum about putting the wiring loom in the dishwasher to clean it. I wonder if that would that work with something like this (ie - does the dishwasher trick clean terminals, or just the oil etc from the outside of the wires) to avoid dismantling?
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Thanks for all the comments folks,
I've given it a proper clean and sanded all contact points. Reassembled carefully and it still doesn't work.
Very weird - it's as if the circular dial is a few degrees out when the unit is assembled. I can get the ignition to turn on when using only the plastic part at the bottom, but when I insert this back into the key mechanism (that has an asymmetric male tab) the key won't turn the ignition on.
I guess they do wear out, and that's why those replacements are available!
If it comes to it, I'll order one from the USA, but ideally I could get this fixed asap. Thanks for sharing the links!
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Sorry to hear that. You seem to have exhausted all repair options, unless it’s possible to compensate for the apparent wear with epoxy or similar.
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Been away for a couple of weeks, so catching up.
I have a ignition switch (with one non original key) off a 78 us import if you want to contact me. Just a few quid to the forum and postage for me.
As the locks didn't match when I got the bike I took a risk and bought an advertised used set from the US and sourced a key in the UK