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Electrical issue

Discussion in 'Norton Commando Motorcycles (Classic)' started by Mreece, Jun 18, 2018.

  1. Mreece


    Jul 6, 2017
    Hey all,

    I am having what I think is an electrical issue. My problem is this. In the first running key position, which I believe is position three with the headlight off, the bike runs fine. In the furthest key position for the bike to run, which I believe is position four with the headlight on, the bike will backfire most of the time and will not start or will not start easy. If I switch from position three to four while running the bike will eventually back fire and then stall out and eventually kills the battery entirely.

    I have replaced the plugs, wires, coils, and ignition switch and has a new battery. It also has a Boyer electronic ignition.

    Could a voltage regulator be going bad?

    What does the zener diode do underneath the seat and behind that battery? Could that be going bad?

    I appreciate any feedback as I am still new to these bikes!

  2. Atlas Commando

    Atlas Commando VIP MEMBER

    Feb 27, 2018
    Lots of knowledgable Boyer users are here. I'm not one of them but it sounds like your system voltage is getting pulled down to the Boyer's threshold when your headlight is on, new battery or not. Have you checked battery voltage in both key positions? As for the zener, that I know a bit about. They are not prone to failure unless... the connection to their heat sink is compromised. The zener converts excess power from the alternator into heat, a part of British motorcycle power management from the era. At low revs or with lights on it is typically doing nothing. It is conceivably a source of your problem, but with my dangerous amount of knowledge I would check battery voltage before and after cleaning up the terminal connections as your next step, then check every connection between the battery and the Boyer and confirm the ground circuit as well.
    Good Luck getting it sorted! If you can use a Norton as your daily transportation for a full year the British Parliament will mail you and Electrical Engineering Degree.
    Northton and Nater_Potater like this.
  3. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Nov 20, 2004
    The Zener is the voltage regulator and that is normally attached on the inside of the RH Z-plate. The item "underneath the seat and behind the battery" sounds like the rectifier (black finned item?).
  4. Mreece


    Jul 6, 2017
    Thanks for the info!

    And yes. I was talking about the rectifier. What does that do? Is there also a capacitor? It's blue in color and has a wire that wraps around it.
  5. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Nov 20, 2004
    It rectifies the alternating current (AC) output from the alternator to direct current (DC) for battery charging etc.

    There is normally a blue 2MC emergency starting capacitor suspended by an anti-vibration spring.

    I suggest you read through the electrical section (J) of the manual.

    Where you see mention of a "35A fuse" note that it refers to the blow rating.
    Only replace with another 35A fuse of the original blow rated type, or use a 15A-20A continuous rated fuse.
    Last edited: Jun 19, 2018
  6. lazyeye6


    Feb 28, 2014
    A new battery is not necessarily a good battery. Even new ones can be bad right out of the box. A Boyer ignition will demonstrate the situation you describe if the battery is low in charge. Check the voltage of the battery (not running) in the two switch positions you describe and
    check back with results. Alternatively pull the battery out and take it to a battery store and they will analyze it.
  7. mdt-son


    Jan 19, 2012

    The switch you mention is the master switch. If you replaced it I guess it is i order, but please check resistance across the switch and between poles and ground in the various positions.
    However, my haunch is that you have a short in the wiring loom for lighting. You need to disconnect the wires at the switch and inside the h/l bucket. Use an Ohmmeter and measure resistance of each wire against ground. If it's an interemittent failure, you need to examine the loom carefullly for scoring marks and tear.

    I hope this helps.

  8. batrider


    Aug 9, 2008
    Another thing to look at is the wire junctions under the tank. Usually the straight-thru inline type are OK. But anything with 3 or more wires connected are trouble. They eventually break internally and don't hold the bullets tightly anymore. Check especially the red ground wire junctions. These parts are all available new.
  9. Peeeleven


    Feb 16, 2017
    I had a similar problem with my Mk3 and after trying various things including swaping from boyer to pazon , new coils, plugs , ign switch etc finaly found it to be the old fuze holder. new blade type one fitted and no more problems.
  10. Mreece


    Jul 6, 2017
    Hey guys,

    I finally got out to the garage to tinker with the Norton.

    I measured resistance across each point of the main key switch to ground.

    White wire had 2.3ohms
    Brown with green stripe wire had 2.3ohms
    Brown with blue stripe has 110.6 ohms
    Blue with yellow stripe had 0.8ohms

    I also measured voltage of the battery while the engine was on and off and at the different key positions

    Non running Voltage goes as follows
    At rest it was at 12.2v
    Position 3 (with lights off) was 12.02v
    Position 4 (with lights on) was at 11.78v

    Running motor voltage goes as follows
    At rest it was at 12.2v
    Position 3 (with lights off) was 12.6v
    Position 4 (with lights on) was 11.89v

    I also measured the amps with the motor off

    At rest I had 0amps
    Position 3 I had 0.7amps
    Position 4 on low beam I had 3.75amps and on high beam I had 5.20amps

    I took a look at the wire harness and found a couple of loose connections. I also found a green with yellow stripe wire that looked like is should have been plugged into what looks like a "warning light assimuator" according to the wire diagram and also had a white with brown stripe wire and a read ground wire plugged into it.

    The only thing that I think seems strange is that my battery doesn't seem to be charging while running.

    Any other suggestions before I start to diagnose the alternator?

    Thanks for the information!
  11. marshg246

    marshg246 VIP MEMBER

    Jul 12, 2015
    I suspect that your meter is not correct. A fully charged 12volt battery should be about 13.2 volts with no load. With the engine running and lights off it should be higher and when throttled up some about 14 volts. If the voltage is not higher when running, you are not charging.

    The warning light assimulator can be completed disconnected without causing problems.
  12. o0norton0o


    Apr 27, 2015
    You need to see the "big picture" to help you diagnose your issue... and that picture is...

    1) Battery- your battery stores voltage which powers your electronix so your boyer is awake to trigger the spark in the proper timing when you kick your bike over. (before your charging system is operating)

    2) Rotor/stator- Your rotor/stator produces current on 2 wires which keep your bike's battery recharging and keep the voltage up when your engine is running (It starts to produce decent voltage above about 1,800 rpms or there abouts)

    3) Rectifier- Your rectifier takes the 2 alternating pulses from each of your rotor/stator leads and through the use of diodes, creates a continuous current of DC voltage which is what your bike uses to power components and to charge your battery.

    4) Zenor diode- You zener diode turns excessive voltage from your rotor/stator into heat, so you don't overcharge your battery or fry your wiring with excessive voltage from overcharging from your rotor/stator.

    SO,... testing is a little bit multimeter and a lot of brain power...

    Lets say you want to test the rotor stator... you clip your test leads on to the battery terminals and start the bike. You see that the voltage is ~12.6 volts at idle. Now is where you think a bit... If you raise the throttle above 2000 rpms, you should see the voltage rise to say,... 13 volts and even more if you raise the rpms more. If your voltage doesn't rise with rpms, you've found a problem. Something is wrong with your charging system.

    BUT, if the charging system responds to RPM, you can test the zener diode while you are there, since charging needs to be working for the zener to do it's job... You raise the rpm's to about 3,000, then while you are looking at the voltmeter, pull the blade connector off the back of the zener diode. The voltage should visibly rise when you unclip the connector. Put it back on and the voltage should instantly drop... If it does that, your zener, your rectifier, and your rotor stator are all working.

    ... And now more brain work... electricity is like a magic trick. You can't look at a wire, like a leaky gasket and see it's not working. It takes some thought to figure out what direction symptoms are pointing you toward... Stuff like a poor battery ground, corroded battery terminal, corroded fuse contact (as was mentioned) all collude to make you crazy when every component seems to test OK, yet you have a problem. At some point, you need to think about what the common denominator might be for the problem you are experiencing...

    Stupid stuff like the battery terminal corrosion, or fuse contact corrosion is probably a consideration in every electrical issue, as are worn out key switch, and a potential skinned wire inside the headlight or passing through a grommet or around the headstock. Grounding the engine is very important on a norton for it's ignition. Isolastically mounted engines make for poor grounding through mount points. Add extra wires from the engine mounting bolts to the frame of the bike...

    Troubleshooting electricity requires as much thought as observation. If all the components test good and you think your wiring is solid, and your fault occurs from certain key switch positions,... I'd be looking at the either the key switch itself OR, some wiring issue on a circuit for the key switch position that has the fault
    Last edited: Jul 11, 2018
    kommando, texasSlick and Bodger like this.
  13. 1up3down


    Jan 12, 2011
    Running motor voltage goes as follows
    At rest it was at 12.2v
    Position 3 (with lights off) was 12.6v
    Position 4 (with lights on) was 11.89v

    looks to me like your battery could well be the problem, it may not be able to hold a load, the voltage is too low to run a boyer with the lights on (11.89) so it spits and backfires

    hook up your volt meter again to the battery and start the bike and increase the throttle until the rpms go up to around 2500 and see what the volt meter says at 2500, it should be up around 14 to show it is actually charging the battery ---- is that is so then good but you still may need a new battery as it may be able to hold the voltage under load with the boyer, have batter load tested
  14. Stephen Hill

    Stephen Hill

    Oct 28, 2009
    Check the voltage going to the Boyer black box when the key is in the position that is giving you trouble.
    If it is low, you could have a battery which can't take the load of a headlight. Or bad connections between the switch and the Boyer.

    Stephen Hill
    pattouno likes this.
  15. everiman


    Aug 22, 2013
    I had a similar problem, farting, backfires, missing, dead battery, dead bike, turned out to be harness wires rubbing on the frame to the point they were grounding. Shorted wires should have blown the fuse, but it didn't. There was nothing wrong with the fuse I was able to blow it in the usual way by accidentally letting negative wire contact positive ground, so I am thinking that somehow the charging system conspired with the battery to keep the fuse from blowing while at the same time emptying the battery and depriving the ignition of the electrons it needed to make reliable sparks. This probably does not make any sense, whatever, once I taped up the frayed wires and secured the wiring harness so it would not rub on anything it has not re occurred.

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