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short circuit at master switch console Mk3

Discussion in 'Norton Commando Motorcycles (Classic)' started by Marcel, Jan 12, 2018.

  1. Marcel

    Marcel

    Joined:
    Aug 8, 2009
    Dear all
    Just wanted to replace the old brake lines on my Mk3 and managed to short the electric cables under the master switch console with my spanner to the headlight shell. Key was in the off-position. Main fuse (5 ampere) has not blown. Now when I put the key in the on-position there is nothing at all going on. Where to look first to solve this problem? Is there a fuse in the headlight shell?

    Thanks for your help.

    Greetings from Switzerland
    Marcel
     
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  2. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    The standard main fuse should be 35A (blow, 17A continuous).


    There is only the one (35A blow) fuse as standard, close to the battery.
     
  3. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    Yes , check the rating of the fuse. The number should be stamped into it. I doubt if it's only a 5 A as it likely would not support the electrical draws of the bike with full lights on and say hitting the horn, so pull it and check again.
     
  4. Marcel

    Marcel

    Joined:
    Aug 8, 2009
    Hello
    Checked fuse again. Has 15 ampere. Put in a new fuse but even at the power point socket there is no power. What should I check next?
    Thanks for your help.
    Greetings Marcel
     
  5. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004

    Assuming the battery is charged and that you have a copy of the Mk3 manual (if you don't then use the pdf copy in the link below) check for volts at both ends of the fuse holder and at each stage along the brown/blue (NU) wire as shown on the Mk3 wiring diagram between battery(-) and ignition switch (terminal 1).


    http://britmoto.com/manuals/Manuals/850_man.pdf
     
  6. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    Also clean up your ground for good metal to metal contact.
     
  7. Madnorton

    Madnorton

    Joined:
    Jun 9, 2008
    Try it at the headlight on position, you may have burnt the contact in the switch when it shorted.
     
  8. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    Yes the switch contact could have burnt just enough upon short to need checkings. Disconnect the NU wire at the switch , run a fused jumper wire from that wire to power up pretty much anything. If good it's the switch. Or test light the disconnected NU wire tracing continuity back to the battery.
     
  9. Marcel

    Marcel

    Joined:
    Aug 8, 2009
    Thanks for your help. Problem solved. There was a second fuse in the line which has blown.

    Greetings
    Marcel
     
  10. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    Two fuses on the same power line. Hmmm....
     

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