http://www.peterrenn.co.uk/archive4.html Features Archive: Joseph Lucas: The Prince of Darkness. (1890s translucent overalls whilst undeniably stylish proved sadly impractical..) So there you are, grubby Haynes Manual in one hand, circuit tester in the other trying to work out why the lights/horn/wipers/cigarette lighter/clock etc. won't work, (apart from the fact that it has 'Lucas' stamped on it that is.) Tracing the circuit usually works eventually but often you find yourself with several loose wires and no clues as to where they go, in which case you need a clue or two. There is a British Standard for vehicle wiring number BS-AU7a which defines the colours and allows you to trace where the wires should go from first principles rather than a diagram. It also allows accessories such as electric fans to be added with the correct coloured wires which assists later diagnosis enormously. None of this helps the fact that the things on the ends of the wires are usually made by Lucas and are therefore of er.. variable quality! I'm particularly fond of a description of an E-type Jaguar's headlamp switch as having" three positions: DIM, FLICKER and OFF. Anyway, that's enough potentially libellous comments (I'm sure all Lucas products are simply fab nowadays and the repro stuff is only crap because it is so authentic :) This info should not only allow you to trace original wires but also to use the correct colours when adding additional equipment like spotlights, ejector seats or whatever. Firstly the basics- What The Colours Mean: BROWN is for direct, unswitched, unfused supply from the battery. Seen on wires to alternators, dynamos, control boxes and ignition switches etc. Always live and often carrying heavy current. YELLOW sometimes used as an alternative to brown on older cars. Also used on solenoids and overdrive switches. http://www.peterrenn.co.uk/archive4.html PURPLE Direct, unswitched but fused supply from the battery. On older cars with no purple wires, brown wires with a secondary tracer colour are used. WHITE Unfused supply from the ignition switch. GREEN Fused supply switched via the ignition switch. Used for things like the wiper motor, indicators and brake lights which only work when the ignition is on. BLUE The main colour for front lights- headlamps and spotlamps. RED The main colour for rear and side lights. BLACK Usual colour for wires from components to earth points on the body. These refer to the main colour of the wire. The second tracer colour which is on many wires is the thinner line and is used to identify the wire. There is a certain amount of logic to them too as you will see. Below is the colour code table for BS-AU7a which was amended in the 'eighties so there will be a few variations on our '50s to '70s cars.. Main colour is given first , tracer second MAINLY BLACK WIRES Black Black/ Brown Black/ Blue Black/ Red Black/ Purple Black/ Green Black/ Light Green Black/ White Black/ Yellow Black/ Orange All earth connections Tachometer generator to tachometer Tachometer generator to tachometer Electric or electronic speedometer to sensor Temperature switch to warning light Relay to radiator fan motor Vacuum brake switch or brake differential pressure valve to warning light and/or buzzer Brake fluid level warning light to switch and handbrake switch, or radio to speakers Electric speedometer Radiator fan motor to thermal switch MAINLY BLUE WIRES Blue Blue/ Brown Blue/ Red Blue/ Light green Blue/ White Blue/ Yellow Blue/ Black Blue/ Pink Blue/ Slate Blue/ Orange Lighting switch (head) to dip switch Headlamp relay to headlamp fuse Dip switch to headlamp dip beam fuse. Fuse to right-hand dip headlamp Headlamp wiper motor to headlamp wash pump motor a) Dip switch to headlamp main beam fuse b) Headlamp flasher to main beam fuse c) Dip switch main beam warning light d) Dip switch to long-range driving light switch Long-range driving light switch to lamp Fuse to right-hand main headlamp Fuse to left-hand dip headlamp Headlamp main beam fuse to left-hand headlamp or inboard headlamps when independently fused Fuse to right-hand dip headlamp http://www.peterrenn.co.uk/archive4.html MAINLY BROWN WIRES Brown Brown/ Blue Brown/ Red Brown/ Purple Brown/ Green Brown/ White Brown/ Yellow Brown/ Black Brown/ Slate Brown/ Orange Main battery lead Control box (compensated voltage control only) to ignition switch and lighting switch (feed) Compression ignition starting aid to switch. Main battery feed to double pole ignition switch Alternator regulator feed Dynamo 'F' to control box 'F' Alternator field 'F' to control box 'F' Ammeter to control box. Ammeter to main alternator terminal Alternator to 'no charge' warning light Alternator battery sensing lead Starter relay contact to starter solenoid Fuel shut-off (diesel stop) MAINLY GREEN WIRES Green Green/Brown Green/ Blue Green/ Red Green/ Purple Green/ Light green Green/ White Green/ Yellow Green/ Black Green/ Pink Green/ Slate Green/ Orange Light green Light green/ Brown Light green/ Blue Light green/ Red Light green/ Purple Light green/ Green Light green/ White Light green/ Yellow Light green /Black Light green /Slate Light green/ Orange Accessories fused via ignition switch Switch to reverse lamp Water temperature gauge to temperature unit Direction indicator switch to left-hand flasher lamps Stop lamp switch to stop lamps, or stop lamp switch to lamp failure unit Hazard flasher unit to hazard pilot lamp or lamp failure unit to stop lamp bulbs Direction indicator switch to right hand flasher lamps Heater motor to switch single speed (or to 'slow' on two- or three-speed motor) Fuel gauge to fuel tank unit or changeover switch or voltage stabilizer to tank units Fuse to flasher unit a) Heater motor to switch ('fast' on two- or three-speed motor) b) Coolant level unit to warning light Low fuel level switch to warning light Instrument voltage stabilizer to instruments Flasher switch to flasher unit a) Flasher switch to left-hand flasher warning light b) Coolant level sensor to control unit c) Test switch to coolant level control unit Fuel tank changeover switch to right-hand tank unit or entry and exit door closed switch to door actuator Flasher unit to flasher warning light Start inhibitor relay to change speed switch; or switch to heater blower motor second speed on three-speed unit Low air pressure switch to buzzer and warning light Flasher switch to righthand warning light; or differential lock switch to differential lock warning light Front screen jet switch to screen jet motor Fuel tank changeover switch to left-hand tank unit; or entry and exit door open switch to door actuator Rear window wash switch to wash pump; or cab lock-down switch to warning light http://www.peterrenn.co.uk/archive4.html MAINLY ORANGE WIRES Orange Orange/ Blue Orange/ Green Orange/ Black Orange/ Purple Orange/ White Orange/ Yellow Orange/Light green Orange/ Pink Orange/ Slate Wiper circuits fused via ignition switch Switch to front screen wiper motor first speed timer or intermittent unit Switch to front screen wiper motor second speed Switch to front screen wiper motor parking circuit, timer or intermittent unit Timer or intermittent unit to motor parking circuit Timer or intermittent unit to motor parking circuit Switch to headlamp or rear window wiper motor feed, timer or relay coil Switch to headlamp or rear window wiper motor parking circuit timer or relay coil Timer or relay to headlamp or rear window wiper motor feed Timer or relay to headlamp or rear window wiper motor parking circuit MAINLY PURPLE WIRES Purple Purple/ Brown Purple/ Blue Purple/ Red Purple/ Green Purple/ Light green Purple/ White Purple/ Yellow Purple/ Black Purple/ Pink Purple/ Slate Purple/ Orange Accessories fed direct from battery via fuse Horn fuse to horn relay when horn is fused separately Fuse to heated rear window relay or switch and warning light Switches to map light, under bonnet light, glove box light and boot lamp when fed direct from battery fuse Fuse to hazard flasher Fuse to relay for screen demist Interior lights to switch (subsidiary circuit door safety lights to switch) Horn to horn relay Horn to horn relay to horn push Rear heated window to switch or relay Aerial lift motor to switch up Aerial lift motor to switch down MAINLY RED WIRES Red Red/ Brown Red/ Blue Red/ Purple Red/ Green Red/ White Red / Yellow Red/ Black Red/ Pink Red/ Slate Red/ Orange Red/ Slate Main feed to all circuits mastered by sidelamp switch Rear fog guard switch to lamps Front fog lamp fuse to fog lamp switch Switches to map light, under bonnet light, glove box light and boot lamp when sidelamp circuit fed Bulb failure unit to right-hand-side and rear lamps a) Sidelamp fuse to right-hand side and rear lamps b) Sidelamp fuse to panel light rheostat c) Fuse to panel light switch or rheostat d) Fuse to fibre optic source Fog lamp switch to fog lamp or front fog fuse to fog lamps Left-hand, sidelamp fuse to side and tail lamps and number plate illumination Sidelamp fuse to lighting relay Lamp failure unit to left-hand side and tail lamps Fusebox to rear fog guard switch Window lift main lead http://www.peterrenn.co.uk/archive4.html MAINLY WHITE WIRES White White/ Brown White/ Blue White/ Red White/ Purple White/ Green White/ Light green White/ Yellow White/ Black White/ Pink White/ Slate White/ Orange White/Yellow (or just plain yellow) Ignition switch or starter solenoid to ballast resistor Oil pressure switch to warning light or gauge, or starter relay to oil pressure switch. Choke switch to choke solenoid (unfused) and/or choke to switch to warning light, or electronic ignition distributor to drive resistor. Starter switch to starter solenoid or inhibitor switch or starter relay or ignition (start position) to bulb failure unit Fuel pump no 1 or right-hand to changeover switch Fuel pump no 2 or left-hand to changeover switch. Start switch to starter interlock or oil pressure switch to fuel pump or start inhibitor switch to starter relay or solenoid Ballast resistor to coil or starter solenoid to coil. Ignition coil contact breaker to distributor contact breaker, or distributor side of coil to voltage impulse tachometer Ignition switch to radio fuse Current tachometer to ignition coil Hazard warning lead to switch a) Overdrive b) Petrol injection c) Door locks d) Gear selector switch to start YELLOW WIRES Yellow (or yellow/white) a) Overdrive b) Petrol injection c) Door locks d) Gear selector switch to start PINK WIRE(!) Pink/ white Ballast terminal to ignition distributor That's all folks. The usual disclaimer applies., ie that This is correct to the best of my knowledge but you use this information at your own risk. So don't sue me if you blow your alternator or fry all your relays...