Headlight & Stop/Start switch Relay install Question
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Thread: Headlight & Stop/Start switch Relay install Question

  1. #1
    Senior Member
    Join Date
    Jul 2009

    Default Headlight & Stop/Start switch Relay install Question

    How is a relay installed to keep the 5 amps that goes through your start/stop switch to prevent burning out the stop/start switch. Im told when you start the bike that the headlight goes out till it starts and this has something to do with it?? At any rate anyone have a wireing diagram of this modification? thanks.

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  3. #2
    Pope "papa" of the VTXOA Chicago-Spike's Avatar
    Join Date
    Nov 2003
    St Charles, IL.


    On the "How To" board in the 1800 Electrical thread, read posts 7 and 8 for the relay install and why it is needed;
    AMA Life Member 721314

  4. #3
    Senior Member
    Join Date
    May 2007
    Graham Tx.

    Default Headlite Relay

    The 5 amp draw thru the headlite will kill the contacts sooner or later.
    Installing a relay will reduce that draw to only what is required to
    activate the coil on the relay (low amp draw). It's a simple install that is well worth the time and effort. Highly recommended. Some install an off/on switch inline from the starter switch to the headlite relay coil so that they can have the bike turned on without having the headlite on when doing maintenance.


  5. #4
    Senior Member
    Join Date
    Jul 2004
    Schenectady NY


    Big Bike Parts makes a switch assembly that mounts on the top of
    the clutch master cylinder.

    If you route the darkblue/white stripe wire from the start/stop
    switch to the BB switch assembly, and route the output of
    one of the three switches to the headlight relay terminal 86
    you can use the switch to turn off your headlight while doing
    engine maintenance.

    You can route one of the other switches to terminal 86 of the
    lightbar relay and use it to turn your lightbar on and off.

    Here is the recommended wiring for the two relays:

    Terminal 30/51 on both relays: 12 gauge red wire coming from
    battery positive thru in-line fuses.
    Headlight fuse should be 7.5 amp,
    lightbar fuse should be 7.5 amp for two 35 watt lamps or
    10 amp for two 55 watt lamps.

    Terminal 87 of headlight fuse to darkblue/white wire input to
    the headlight high/low selector switch.

    Terminal 87 of lightbar relay to lightbar lamps

    Terminal 85 of both relays to ground.
    You can use any solid green wire on the bike for ground,
    or the battery negative terminal, or the unpainted chassis
    of the bike.

    Terminal 86 of headlight relay from switch that you selected as
    headlight on/off switch

    Terminal 86 of lightbar relay from switch that you selected as
    lightbar on/off switch.

    If you are required to automatically turn off the lightbar
    when your high beam is activated instead of installing the
    BB switch assembly in series with the darkblue/white stripe
    wire that would normally connect the output of the
    start/stop switch assembly to the left handlebar switch assembly,
    connect the BB switch assembly in series to the white
    wire output from the high/low selector switch.
    This will allow you to conform to the NHTSA regualtions,
    but you will only be able to switch your lowbeam off
    for maintenance purposes, and you will require a third
    relay if you want to have your high beam on a relay.
    Last edited by Coyote7864; 05-19-2010 at 12:26 PM. Reason: correct typos
    2003 VTX1800 C model Retro fenders

  6. #5
    Senior Member
    Join Date
    Jul 2009


    You all are the Bomb! thanks much.

  7. #6
    Senior Member
    Join Date
    Jul 2009


    One other thought I have,,why in the hell didn't Honda fix this knowing it will cook the start/stop switch.There seems to be no end to the fixes that are needed.

  8. #7
    Senior Member
    Join Date
    Aug 2008
    RI 03C


    Stock C headlight with basic 20 amp, single pole, 2 terminal toggle switch inside, no relay, works great.
    Heavy red/black wire from hdlt fuse and smaller red/black wire from start switch on 1 terminal, blue/white wire from hi/low beam switch on the other, no automatic hdlt, fine with me, manual control and saves start switch.
    Last edited by 369; 05-22-2010 at 05:49 PM.

  9. #8
    Senior Member dbx's Avatar
    Join Date
    Mar 2008


    Quote Originally Posted by 369 View Post
    Stock C headlight with basic 20 amp, single pole, 2 terminal toggle switch inside, no relay, works great.
    I just did the same thing, and now my headlight is brighter than before, with same old original bulb.
    Must be getting more current by not going to the start switch and back through those chincy 22awg wires.
    I was going to put a relay in, with a switch, then figured since I only have the single 55/60 watt light, a toggle on the headlight housing is all I need, compact w/black lever blends right in.
    It's easily reached just under the top triple tree, out of sight, you'd never know it was there.
    Last edited by dbx; 05-22-2010 at 02:33 AM.

  10. #9
    Senior Member
    Join Date
    Jul 2004
    Schenectady NY


    The reach over the handlebars to the headlight housing is
    too long for most of us. For safety reasons, it it best to
    have the switches within a thumbs reach of the hand grips.

    It is for that reason that most of us install a relay.
    The relay allows a switch capable of handling only
    a small current to control a larger amount of current
    thru the main relay contacts.
    You can hide the relay anywhere out of sight,
    but I usually recommend the "secret" toolbox door
    under the left painted sidecover as it is convenient
    to the battery positive terminal.

    The headlight shell appears to be plenty big, but there
    are an awful lot of wires and large multipin connectors
    already hidden inside it, and finding a good spot for
    a large toggle switch can be tricky.

    Then there is the resale value of the bike to consider.
    The stock handlebar switches look a lot neater than
    a toggle switch mounted on top of the headlight shell.

    But to each his own.

    I have even tried to help other forum members to install
    Harley Davidson switch assemblies and custom
    switch assemblies (like Jokers) made for Harleys on our
    bikes. The main reason to go with Harley switch asemblies
    is if the owner is already familiar with the Harley layout,
    but they are also very convenient if you want to install
    apehangers on your bike because the Harley switch assemblies
    come with wiring about three feet long, much longer than
    the stock VTX handlebar switch assemblies.

    The Custom switch assemblies look almost like there
    are no switches present at all. Really clean!
    2003 VTX1800 C model Retro fenders

  11. #10
    Senior Member mrmustang69's Avatar
    Join Date
    May 2008
    Perry, Fl.


    I helped Gary1945 do this to his bike this weekend, but is there a way to actully test to see if this is workking after you rewire everything ...everything worked after we get it back together WHEW. but how can i test to see if the draw has been decreased? thanks Dana
    Don't run your fingers over my bike ,and I won't run my bike over your fingers!!!
    '03 1800 c .Hard krome sideburners,desmog,ground fix,pair vaule blocked, baron X bars,quick release back rest, flame mirrors, pcIII,MS fats shield and lowers,iso grips and throttle boss, darkside GYTT,corbin young guns seat...more to come ...

  12. #11
    Senior Member
    Join Date
    Jul 2004
    Schenectady NY


    If you went to your local community college to get your associates degree
    in electrical construction and maintenance or electronics design and
    repair, then you would know about Ammeters which require you to break
    the circuit apart and put the Ammeter into the circuit in series with the
    load (headlight or lightbar). There are also clamp-on Ammeters which
    do not require you to break the circuit apart, but do require you to
    isolate the wire that you want to measure a distance away from
    all the other wires that would normally be near it in the wiring harness or
    in the headlight shell or under the painted sidecovers.

    Clamp on Ammeters
    have a large clamp that you put the wire thru and measures the amount
    of current thru the wire by the strength of the magnetic field generated
    by the current moving thru the wire. You would want to have the
    headlight or lightbar switched on so that there would be
    measurablle current thru the wire when you read the Ammeter.

    Did you get the master cylinder mounted switch unit that I recommended?

    The current into that switch assembly on the red wire should measure
    about one half to one amp depending on whether you are powering only
    a single headlight relay, or two relays, one for the headlight and
    one for the lightbar. Some relays only require one quarter amp of current
    to activate the coil, others a half amp. I did not specify any particular
    relay so I cannot be sure of the specs on the relay that you chose to use.

    The three output wires from that switch assembly are
    yellow for the left switch
    black for the center switch
    blue for the right switch

    Each of those wires that was connected to the coil
    of a relay would measure a fraction of one amp, if you had the
    Ammeter to measure them.

    The most common way for a relay to fail, is for the coil to burn out.
    In that case, the light that you want to switch on or off will not
    light up, and you will need to replace the relay.

    The other way that some relays will fail is that the switching contacts
    will get welded together, and you will not be able to turn off the light.
    If you installed an inline fuse holder between relay terminal 30/51
    and the positive battery terminal, you can remove the fuse to turn out the light and prevent the battery from being drawn down
    by the light when the engine is turned off.
    2003 VTX1800 C model Retro fenders

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