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Headlamp hell

Discussion in 'Norton Commando Motorcycles (Classic)' started by Rhombeus, Apr 23, 2019.

  1. Rhombeus


    Apr 23, 2019
    Hi all,

    My first post, bar the images I just uploaded into the picture thread and it's a plea for advice.
    Last Saturday I rode home from a mates at 1am.
    The main beam died and left me with a very dim dip beam. Not only that but the dip was flickering, it was so dull traffic lights were blinding in comparison.
    Also If I accelerated over 50 mph the light would just go out altogether.
    Luckily it was a very clear night and bright full moon.

    It's a Halogen set up and I have a new bulb on order but I have nasty feeling the problem may be more than that.

    Have any of you chaps had this issue before?
  2. gtiller

    gtiller VIP MEMBER

    Nov 5, 2012
    Welcome onboard @Rhombeus!

    Always check your earth as a starting point.

    If your earth wire is breaking down, you’ll be making the connection through the clutch cable outer or through the greased up steering bearings, which isn’t ideal.

    Make up a heavy cable with a crocodile clip on each end - attach one end to the battery positive terminal, and the second to one of the bolts holding your headlamp shell in place, and see if your lights get brighter.

    It’s always a good variable to rule out before you starting digging deeper and unbolting things.
  3. Nater_Potater

    Nater_Potater VIP MEMBER

    Apr 7, 2013
    Lucas, Prince of Darkness, strikes again! It could be a number of things (of course). Make sure you have a good ground to the bulb, as no amount of power to the bulb will do any good if it can't find its way back to earth. There's potential for resistance at the ignition switch, handlebar dip switch, headlamp socket contacts, ad nauseum...
    Assuming you have a good battery (or hook a charger to it while testing), does it operated properly with the engine off? As you're probably aware, vibration plays hell with the 45-year-old wiring insulation and bullet connectors. If it works properly in the shop, start tugging cables to see if you can get things to flicker. The fact that it goes out over 50 mph makes it sound like it's something other than the charging system, but don't count that out, either!
    Search for a manual that covers your year (what year is your bike?) for an electrical diagram. That'll give you an idea where some pesky connector might be giving you trouble.

  4. gtiller

    gtiller VIP MEMBER

    Nov 5, 2012
    Looks like you have a MK3 from your pic

    MK3 Commando Wiring.png
  5. Craig

    Craig VIP MEMBER

    Dec 20, 2005
    If vibration makes things worse I might start fooling with switch connections , bar mounted dip switch first on list ....
  6. Tornado

    Tornado VIP MEMBER

    Dec 5, 2017
    I've been messing around trying to sort out an issue with a new LED double-dipper main lamp. After reassembling the whole headlamp unit, had the main fuse blow out twice in quick succession. Not sure I resolved it but checked the bullet connectors and found one or two where the metal terminals protruded slightly from under the plastic cover...so maybe an errant short with the shell or another wire was blowing the fuse.
    Still have my original issue with the LED....runs fine dip(low) and high (main) beam if an only if I first remove the high beam warning lamp. With the warning lamp in circuit, LED is always on main beam. Tried an diode on the warning lamp but didn't fix it.
  7. Rhombeus


    Apr 23, 2019
    Thanks for all the help.
    This really gives me a good starting point, I just wish a was more au fait with electrics.
    Time to learn!!
  8. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Nov 20, 2004
    I suggest you start with the easy things.

    The logical thing to do would be to remove the bulb and check if (one?) of the filaments has blown or if there are signs of cloudiness or blackness on the glass. Then check both filaments with a 12V battery.

    Had a similar thing happen when the bulb glass became loosened from the metal base.
    Last edited: Apr 23, 2019
  9. Steves


    Oct 16, 2016
    Get yourself a multimeter. They are cheap enough off eBay. I had a similar not exact problem, connector loose at back of ignition switch.
  10. Craig

    Craig VIP MEMBER

    Dec 20, 2005
    Short of multi-meter , a plain old circuit tester , alligator clip on one end a pointer with light on other , easy/simple to use and may be all you need for this issue....

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