Service Bulletin: New Handlebar Ignition Cut-Out Button

Service Bulletin: New Handlebar Ignition Cut-Out Button

Triumph Handlebar Ignition Cut-Out Button Service Bulletin

Triumph Service Bulletin #13 1-29-1966

Dated January 29, 1966, this Triumph service bulletin #13 goes into detail regarding the new handlebar cut-button on ignition model twin cylinder motorcycles. This cut-out button was fitted on the right hand side of your handlebar near the throttle assembly. There where two different types of cut-out buttons used on 1966-1967 models but both look strikingly close. This service bulletin and this post will inform you on how to spot the two different cut-out buttons as they should not be interchanged.
Triumph Cut-Out Kill Button

Lucas "mammoth" kill button assembly

The new cut-out button that Triumph is referring to is pictured above. Many folks and restorers call this cut-out button the "mammoth" kill switch due to it's rather large unusual size. This specific cut-out button is correct for Triumph T120TT, T120C, TR6C and the T100SC models that featured A.C. ignition from 1964-1967. What makes it "correct" for A.C. models? The answer lies in the color of the plastic button, it's black - seriously.
Triumph Black Button Kill Switch

Lucas black cut-out button

The kill switch that had a black color button is only correct for A.C. ignition models. Not just because the button color but because the buttons specific function. The black button has "normally open" contacts which should only be used with A.C. ignition models.
Lucas Brown Button Kill Switch Button

Lucas brown cut-out button

The kill switch with the brown plastic button is correct for models that where equipped with standard ignition from 1966-1967 which included the Triumph Bonneville T120R, Triumph Tiger TR6R, Triumph Daytona T100R, and others. Typically under Lucas part number 35601. The brown button has "normally closed" contacts.
Lucas Button Bottom Terminals
Measure continuity between each terminal

If you are not sure exactly how to identify each kill button, you can measure continuity between each terminal using a meter. The black button (A.C. ignition) will not show continuity when grounded. The brown button (standard ignition) will show continuity to both terminals when grounded or when the button is pushed.

"Brown is for standard & black is for A.C..."

I hope this post was somewhat of an eye opener as I have seen many folks get the two buttons confused with each other. Remember the brown button is for standard ignition and the black colored button is for A.C. ignition. Thanks for reading today's post.


  • Doug Holley

    I purchased two of the “brown” button 35601 for my 1967 Triumph T100R and T100C converted to a battery system. Because they hard to come by, I paid dearly for these. Above, the description says the “brown” button switch has “normally closed” contacts. It does not. The contacts are “normally open” and make momentary contact when the button is pressed and grounds the switch, where the black button does not. All well and good with battery and points ignition as in 1967 but not good for modern electronic ignition systems like Boyer, etc. In a positive ground system, the white wire of the Boyer box through a momentary “normally closed” switch will break the connection and stop the engine. The 35601 “brown” button will not complete the connection unless pressed but grounding the Boyer box destroys it. So beware. Normally closed switches are available to fit the “mammoth” handlebar housing (3/4") for about $10 from Amazon. Some careful fabrication with 15mm dia. Delrin can extend the button height to very closely match the original.
    I have two, NOS 35601 “brown” buttons available in their original box for restorers with battery ignition (w/points & condensers) B & C range twins.

  • Buzz

    working on installing new harness on friends 72 T100R, got everything just about done but kill button is confusing , wires are different colors one should be white the other blue , regardless on this bike should one be grounded to the red and other to the white ?? have not tried to hook up as of yet don’t want to short anything out, wiring diagram would be help thanks

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