No voltage to Low Beam Headlight

Discussion in 'General' started by whereshaldo, May 7, 2018.

  1. whereshaldo

    whereshaldo Member

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    I've got an odd issue in that the low beam headlight is not working and used to work just fine. Bulb is not burned out and so I'm at a loss as to what would lead to this other than a switch failure or a broken wire. Am I missing something? It seems like power comes in to the switch on the Common Yellow wire and then either runs to Blue (hi beams) or White (low beams).

    Is it really that simple? If so, I'll pull off the handlebars and make sure there is continuity on the white wire from the switch to the headlight

    Hal
     
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  3. racerx

    racerx Administrator
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    You are correct, the yellow lead feeds AC to the dimmer switch...via the key switch. What happens when you swap the blue & white leads...i.e. connecting B-to-W & W-to-B?

    The fact that you're getting power to the high beam pretty well eliminates anything upstream of the handlebars as the problem. In my experience, dimmer switch failures have been rare. That doesn't leave much for you to check...and all of it is easily accessible.
     
  4. whereshaldo

    whereshaldo Member

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    I keep digging into this and its maddening! For background, I have one of the aftermarket headlights with the socket and removable bulb. Voltage to the switch. Voltage to the white and blue wires in the handlebars. If I plug in the socket i get 5.6v on the high beam when switched to that position both grounded to the chassis and grounding against the socket. Same for the low beam, 5.6v. But when its all assembled I only get the high beam, low beam doesn't work. If i switch the wires, so that blue out of the harness goes to white in the socket, I get low beam, but then don't get high beam with the low beam power running to the high beam.

    Should I be checking something other than simple voltage?

    h
     
  5. kirrbby

    kirrbby Well-Known Member

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    Sounds to me like your switch is bad. Check the switch...see if it switches.
     
  6. whereshaldo

    whereshaldo Member

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    The switch does switch and sends voltage to each of the two location. When on low beams I can measure 5.6v all the way out to the socket. When on high beams I can measure 5.6v all the way out to the socket. I took the switch all the way apart over the weekend and cleaned all the contacts in the switch. The switch appears to function normally but it doesn't give me low beams. I may try just touching the wires to the bulb and see what happens.
     
  7. kirrbby

    kirrbby Well-Known Member

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    Do all of your wires AND wire colors match the wiring diagrams. Could you be connecting the switch wrong...wires swapped?
     
  8. kirrbby

    kirrbby Well-Known Member

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    Does the aftermarket HL have a extra wire? Green? Did you run it to a frame ground? Or a ground wire in the harness?
     
  9. whereshaldo

    whereshaldo Member

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    Yes the harness is all stock with the exception of the relay for the starter. Honda terminals, I actually replace a couple that seemed iffy, and soldered the connections before crimping. Same for the ground wire for the socket. I would be more suspicious of the socket ground except that the high beam works fine. Its possible that the low beam wire is grounding out on the socket -- i guess if i ran it like that for a bit, I could feel whether it got hot. The ground runs to the harness, but I'm thinking of adding a ground to the chassis as well. More ground is not a bad thing.
     
  10. kirrbby

    kirrbby Well-Known Member

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    81 C70

    I would first test the bulb with a continuity tester...everything with a continuity tester.

    One lead touching the bulb housing...then touch each of the contacts one at a time. They should both show continuity.

    Then put the bulb in the socket with the socket unplugged...completely, test the same way with one lead on the ground wire, then touch the blue wire, and the white wire, both should show continuity...bulbs good and socket is good.

    Then test the switch with the 3 dimmer wires disconnected. Yellow is the common/hot wire. So one lead on the yellow, then touch the blue and flip the switch to high beam. It should have continuity when it's on high, then lose it when you switch to low.
    Then touch the white wire, continuity on low, none on high...switch is good.

    Then you need to confirm there is power coming in to the yellow wire on the switch, if there is, everything should work.

    Everything should work provided the sockets green wire is getting a ground.
     
    allenp42 likes this.
  11. whereshaldo

    whereshaldo Member

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    That's good advice. I will dig in some more.

    Its all fun and games until you start using a hammer for electrical work
     

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