British Motorcycle Wiring Colors

Most Vintage British Motorcycles used wiring harnesses and components from Lucas. Therefore, the wire colors are more or less consistent across brands. The table below covers most wire colors used and attempts to say how they were used. Where there are known differences from the standards, those differences are mentioned in the notes column. Published with permission from Greg Marsh Enterprises.
Wire Color Stripe Color Color Code Where Used Notes Examples
Black B Ground on Negative Ground Machines Most machines are positive ground and have no black wires. However, some harnesses (probably after-market) used black instead of red!
On some Triumphs, the horn to ground was Black.
On Triumphs with a horn relay, the relay to horn wire was Black and the horn ground wire was also black.
Color Code: B
Black B Voltage Regulator Negative Output PODtronics, Tri-Spark MOSFET, and most others Color Code: B
Black Red BR Contact Breaker to Center Cylinder's Coil, Triples Color Code: BR
Black White BW Contact Breaker to Timing Side Cylinder's Coil, Twins/Triples On singles, this is the Contact Breaker to Coil wire. Color Code: BW
Black Yellow BY Contact Breaker to Drive Side Cylinder's Coil, Twins/Triples Color Code: BY
Green G Dynamo Field Only on Magneto machines Color Code: G
Green Black GB Stator Low Output (RM19), One Leg (RM24) Color Code: GB
Green Red GR Lefthand Turn Signal Color Code: GR
Green White GW Righthand Turn Signal Color Code: GW
Green Yellow GY Stator High Output (RM19), One Side (RM21), One Leg (RM24) On Norton, also goes to the Warning Light Assimlator Color Code: GY
Light Green Brown LGN Turn Signal (Direction) Switch (Handlebar) common to Flasher Unit Color Code: LGN
Brown N Stop Light Color Code: N
Brown Black NB Horn button to horn (See PB Below) Triumph "usually" used this for the horn. Some used PB Color Code: NB
Brown Green NG Taillight, Pilot Light, Speedo & Tach Illumination Color Code: NG
Brown Blue NU Battery to Ignition Switch if no Ammeter or Battery to Ammeter and see NW Color Code: NU
Brown White NW Ammeter to Ignition Switch I use 14 gauge wire for this and NU Color Code: NW
Purple Black PB Horn button to horn (See NB Above) As far as I know, this color was always used on Norton Color Code: PB
Red R Ground on Positive Ground Machines Some harnesses replaced this with black, but that is not common. Color Code: R
Red Black RB Lighting Switch to Pilot Light On later bikes, this was changed to Brown/Green so the pilot light was on whenever the tail light was on Color Code: RB
Red Green RG Oil Pressure Switch to Oil Pressure Indicator (Red) Triumph before KE00001, after see WN Color Code: RG
Blue U Light Switch (Headlight) to Dip Switch (Handlebar) Some Norton harnesses also use Blue instead of the Blue/Yellow from the headlight switch to the ignition switch Color Code: U
Blue Red UR Dip Switch (Handlebar) to Dip (Low) Beam Color Code: UR
Blue White UW Dip Switch (Handlebar) to Main (High) Beam Color Code: UW
Blue Yellow UY Ignition Switch to Headlight Switch Some Norton harnesses use Blue for this instead.
On Triumph, to stop confusion I use this from the switched side of the ignition switch to pin 4 of the 3-position headlight switch. Some Triumph diagrams have it as NB and some as NW - in either case that is confusing because they are primarily on the "hot" side of the switch.
Color Code: UY
White W "Hot" when the igniton is on. Goes to each handlebar console, the brake switches, and if no kill button, the coils. See WY Color Code: W
White Black WB Contact Breaker (Distributor) to Ignition Coil Only on Magneto machines. Note: The Norton MKIII workshop manual wiring diagram incorrectly shows this instead of Black/White as the timing side contact breaker to coil wire. Color Code: WB
While Green WG Stator Common (RM19 & RM24), One Side (RM21) On Norton MKIII this also goes to the Warning Light Assimulator Color Code: WG
White Brown WN Warning Light Assimulator to Charging Indicator (Red) This is standard for a Norton but I remove the assimulator and install an oil pressure switch connected to this wire. Color Code: WN
White Brown WN Oil Pressure Switch to Oil Pressure Indicator (Red) Triumph from KE00001 on Color Code: WN
White Purple WP Ballast Resistor to Ignition Coils Norton Color Code: WP
White Red WR Starter Switch (Handlebar) to Starter Selenoid Norton MKIII, Triumph T160 Color Code: WR
White Blue WU Under tank junction to ballast resistor Norton, See WY Color Code: WU
White Yellow WY Engine Kill (Handlebar) Triumph Twins/Triples when no balast resistor is used: To coils. Norton Commando, Pre-MKIII: To junction under tank where it connects to the White/Blue which connects to the balast resistor. Norton Commando MKIII: To the balast resistor. Color Code: WY
Yellow Y PODtronics single or three phase input from stator Color Code: Y
Yellow Y Dynamo Output Only on Magneto machines Color Code: Y