If the freedom of speech is taken away then dumb and silent we may be led, like sheep to the slaughter.

- George Washington

Tuesday, 8 February 2011


Sometimes I think I understand motorcycle electrics, and then something comes along to disabuse me of that innocent but inaccurate notion.. Electrics ought to be completely logical, but in practice the 'smoke theory' makes as much sense as anything.
When, for example, the smoke escapes from an electrical component (i.e., say, a Lucas voltage regulator), it will be observed that the component stops working. The function of the wire harness is to carry the smoke from one device to another; when the wire harness "springs a leak", and lets all the smoke out of the system, nothing works afterwards.
I'm on nights at the moment. I rode home on Saturday morning and parked the bike up outside the house. When the time came to go back to work on Saturday evening, I togged up, put my bag in the topbox and switched the ignition on. Nothing. No dash lights, no starter, no go. The ignition switch is a bit dicky, so I fiddled with the key a few times, but then gave up and took the car. (Yes, I checked the kill switch!) This afternoon, after my sleep, I thought I would see what was wrong.

The Yamahaha, being a trail bike, has a very simple electrical system [1]. There is a wire from the battery to the ignition switch, with a fuse close to the battery end. That fuse, just the one, protects every circuit on the bike. A quick check with a test lamp showed that there was juice in the battery, and as far as the near end of the fuse carrier. Then I checked the far end of the fuse carrier and there was still power. So I now suspected a break in the wire under the tank, or a malfunction with the switch itself. Investigating that was going to involve some dismantling, so I decided to do a few easy things today before work, and leave the other stuff to my next day off.

So I took the fuse out to check it. Remember that there was power both before and after the fuse, indicating that the fuse was good, and the fuse itself was unblown. I took the fuse out - all OK - and put it back. I checked the ignition switch, more in hope than expectation, as there was no reason to think anything would be different, and lo and behold there was light. The bike started first time, all the lights worked, and everything was back to normal. So I took out a perfectly good fuse, put it back, and solved the problem.

I know why. The fuse lives in a little box next to the battery, a space which is also shared by the indicator relay. Last week I replaced the relay, as the old one was flashing like a Club 18-30 disco at about 300 bpm. The fuse was simply sulking, as it hadn't had any attention.

It's fine now.

[1] Simple is good, but the disadvantage is that, if the fuse ever blows for any reason, it takes out the engine and lights, everything. I had the headlights fail on a car once, and managed to find a safe place to stop using the indicators. On the Yam, even that wouldn't work. It's a poor design for a bike that is mainly used on the road, and if I ever get round to any serious restoration work on the bike, I'm going to try to design a new scheme that doesn't have all the electrical eggs in one basket.


  1. Had a CX-500 (Aye I know, I KNOW...) once that kept having the same problem. So I welded (soldered) a couple of panel pins in place of the fuse.

    After that never a problem. ran for a good 11 years afterwards, till I scrapped it.

  2. Furor is right. About fifty years ago my father had a car called an 'Isis' that kept blowing a main fuse. He solved the problem by wrapping a nail in cigarette packet foil and jamming that into the fuse holder. The fuse never blew again.

    Mind you, the heater caught fire. But that in itself does not invalidate the principle here - unless you have heated grips maybe.

  3. Ah... a Morris ISIS - it was a variation of the Oxford if I remember correctly. If it was anything like the early Mini I had, there would be a couple of fuses in a crude holder under the bonnet, exposed to all the crap blown in through the grille. The fuse end caps and the contacts would corrode, and the clips would loose their "spring", resulting in very erratic continuity. As Jim says the old foil trick was a common solution.

    As to the Yamaha problem - it's possible that the test lamp was drawing so little power that a poor contact on the fuse didn't show up, yet it would not pass enough current to run the rest of the bike. This can be a particular problem when using a meter (especially a DVM which draw virtually nothing).

    It's not just basic machines like that which have poorly thought out wiring - my BeeEmm had a joint inside the harness, and under the tank, which is part of the main feed to the ignition switch. This gave me much head scratching until finally failed completely. I rebuilt the harness and ran separate wires to eliminate this weak spot.

    And it happens on cars as well, the Italians have form. My old Panda suffered from intermittent total electrical failure - except the engine continued to run. It turned out that the main earth lead runs in one length from battery to the body, then the engine. However the body terminal is just crimped round the conductor where a section of insulation is removed. This corrodes, isolating the car wiring, yet leaving the engine running perfectly!

  4. Furor: nowt wrong with them Maggots! They were held to be slightly uncool at the time, but couriers are still suing them, and I hear at least one has gobe RTW.

    Jim: I've used the foil and/or nail trick a few times myself, but the fire risk always makes me nervous.

    MD: yep, I kind of reckoned it was a high-resistance contact. It would pass enough current to light the test lamp, but powering up the coil and everything else was too much. Funny how it should happen within the space of about 11 hours, as it was running fine before. Today's task is to go round and clean every contact I can get to, and apply liberal quantities of dielectric grease. The Triumph came with every single connector full of it, and I think that's the factory rather then a scrupulous PO. Electrics on that bike are A1.

  5. 'Suing them'?? Well, maybe, but 'using' would be the more likely.

  6. I once had an electric drill that behaved like that, worked every time I tested it but refused to run as soon as I tried to use it.
    Had me beat for days, then I too changed a perfectly good fuse, and problem solved! A badly made sealed cartridge fuse that lost connection as soon as significant power was drawn thorough it.

  7. 'Gobe' = 'gone'. Perhaps I should refrain from posting until fully awake.

  8. @ Woodsy - see? It's magic, I tells 'ee.

  9. I had a CX650 and, miraculously, it didn't do that...

    If I may correct your earlier typo: "[CXs]... were held to be DEEPLY COOL at the time". And their riders were revered amongst true men and women everywhere.

    At least, that's how I remember it.

  10. Pity you can't do a whitewash job on Jawa. When you lot were swanning about on cool Japanese stuff, I was riding an Eastern Bloc dinosaur - cheap, and not even worth that.

    Eee, we used to dreeeeeeam o' riding' a CX500 ...

  11. XX endemoniada_88 said...

    I had a CX650 and, miraculously, it didn't do that...

    If I may correct your earlier typo: "[CXs]... were held to be DEEPLY COOL at the time" XX

    Always fancied a CX 650. But non were ever for sale at the right time and price.

    500s were great. NEVER (except for the electrics I wrote about) ANY problem.

    I got my first in 1985, so I reckon the "cool" had gone out of them by then.

    Na maybe ONE problem. The front wheel did NOT like wet manhole covers (or gravel) at all. On my way to work there was one at the end of Manor Road, Wallasey, turning right outside the Mariners home, which was PERFECTLY aligned to the tracking JUST before you picked it back to the upright to come out of the turn.

    Never came off, but a few close shaves.

  12. Oh aye. Richard.

    I used my two for despatch as well (Pony from the Cunard buildings in Liverpool). Tried the Z-650 a few times, but the CXs had them beat.

    Thzen got a Virago 535. Bloody USELESS. The seat looks GREAT, but after 30 miles you PRAY for the next service station, then EVERY services, JUST to give your ass a rest. Gave me a bad case of sciatica did that one.

  13. Furor - My front wheel particularly hated white lines, especially in the damp. I always put it down to the dreadful Pirelli Bakelite tyres, but maybe it was more than just that!

  14. Have you ever been along dock Road and over the bridges at Birkenhead?

    Railway lines all the way! At the end of the Four bridges, on the Birkenhead side, the lines take a left curve to the sidings by the Cunard wharf, and the RMR H.Q.

    THAT can be fun.(Unless in the twenty years I have been away they have uprooted them).

    Also, any one coming to Berlin. Especially in the East sector. Tram lines! And all over, cobbled side streets.

    FORGET a CX here. Or any of the 500/4s, or Brit bikes, with the narrow front wheels.

  15. XX At the end of the Four bridges,XX

    And Duke Street Bridge.

  16. I ought to be thankful I live in the rural bit, where all we have to worry about is slurry from the fields and the odd patch of diesel. Tramlines and cobbles together is a recipe for a tightening of the old sphincter, for sure.

    The Virago looks very comfy. An ex-colleague had one, and swore it was the comfiest bike she'd ever had, but she wasn't a long-distance rider. The only bike I've ridden with that kind of seating arrangement was a brief run on a Harley Sportster, and I could tell within 100 yards that it would kill my back in shiort order. Comfy up to 10 miles, torture thereafter.

  17. Worst 'leccy problem I suffered, was on a 1965 CB72.

    Used it to commute (down Monday, back Friday) to college. Suffered headlight problems one week. They'd work when the bike was stationary, but not when riding it.

    Turned out there was an earthing fault; but why it wouldn't earth through the head-bearings has me puzzled to this day.

  18. Furor - Cobbles on a CX...no, thank you!

    My most annoying electrical fault was with a Suzuki GSX550. It would blow the main fuse every time the right indicators were used, and continued to do so even after replacing both indicators, the switchgear and all the wiring in between. After which I lost patience and traded it for the aforementioned CX.

  19. Sod's Law ... I set off for a 35-mile ride to visit a neighbouring bike club for their fortnightly meet, and the XT started misfiring almost as soon as I had left the drive. I chanced it for a mile and then turned back. 30 miles of the A40 is a dark place to have a breakdown. I dug the Triumph out of hibernation and used that instead. Great to give it a run out (although I'll need to clean it tomorrow), but then on the way home that started misfiring as well.


  20. Somebody up there is watching you....

    And, apparently, has internet access as well!!

  21. I should have 'touched silicon' as I wrote it.

  22. Give Paris Hiltons tits a grope you mean?

  23. No thanks. Hard to believe, but I do have some standards.

  24. I recall trying to troubleshoot a former friend's MGA (1961?) and discovering that the Ammeter was the only fusible link in the battery feed....it was quite spectacular and shocking to me at the time. We don't speak now but that is for other raesons (I think).

  25. Was that by design or a bodge by a 'previous owner'? It seems remarkable remiss of the designers to forget something as basic as that.

    Shocking, indeed.

  26. Did they ever find a fix for the electrickery on the Guzzi and Ducatis?

    Besides replacing the whole loom with a Suzuki one?

  27. Yes, an easy one. Don't go out in the rain.

    Modern Ducatis seem to have it licked, although mine decided to show me a bit of heritage by chucking its fuel pump under warranty. As this was located in the deepest recesses of the tank and required about an hour's labour to get it out, my dealer first told me it was spark plugs and changed them. When that didn't work, he fixed the pump - but still charged me for the spark plugs, as 'well, I can't take them back, can I?' I didn't pay, but it was a source of some friction between us.

    My Moto Guzzi, funnily enough, was 100% reliable on the electrical side (factory standard, no mods) but needed its carbs balancing about every 1000 miles, just to keep me awake.

  28. It was by design...obviously (!?) the starter/solenoid battery feed did not go through the ammeter but all the other services fed through the ammeter and that main circuit was not otherwise protected by a fuse. So if the short to earth is before the rudimentary fuse box the ammeter glows incandessant and expires in a puff of Smiths smoke.

  29. I know how the ammeters were wired in, but I'm sure they were normally protected by a fuse between the battery and ammeter. Perhaps these were special expendable ammeters. Nice to see you have fully grasped the smoke theory!

  30. XX Richard said...

    Yes, an easy one. Don't go out in the rain.XX

    I lived in Glencoe at the time. NOT possible.

    It was either raining, or going to rain. (Add snow for seasoning).

    Swapped it for a GS 550 eventually and turned it to a Caf racer.

  31. I'm in Wales. Same applies. Damp and corrosion are playing havoc with the Yam at the moment.


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