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
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.
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
Black All earth connections
Black/ Brown Tachometer generator to tachometer
Black/ Blue Tachometer generator to tachometer
Black/ Red Electric or electronic speedometer to sensor
Black/ Purple Temperature switch to warning light
Black/ Green Relay to radiator fan motor
Black/ Light Green Vacuum brake switch or brake differential pressure valve to warning light and/or buzzer
Black/ White Brake fluid level warning light to switch and handbrake switch, or radio to speakers
Black/ Yellow Electric speedometer
Black/ Orange Radiator fan motor to thermal switch
Blue Lighting switch (head) to dip switch
Blue/ Brown Headlamp relay to headlamp fuse
Blue/ Red Dip switch to headlamp dip beam fuse. Fuse to right-hand dip headlamp
Blue/ Light green Headlamp wiper motor to headlamp wash pump motor
Blue/ White 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
Blue/ Yellow Long-range driving light switch to lamp
Blue/ Black Fuse to right-hand main headlamp
Blue/ Pink Fuse to left-hand dip headlamp
Blue/ Slate Headlamp main beam fuse to left-hand headlamp or inboard headlamps when independently fused
Blue/ Orange Fuse to right-hand dip headlamp
Brown Main battery lead
Brown/ Blue Control box (compensated voltage control only) to ignition switch and lighting switch (feed)
Brown/ Red Compression ignition starting aid to switch. Main battery feed to double pole ignition switch
Brown/ Purple Alternator regulator feed
Brown/ Green Dynamo 'F' to control box 'F' Alternator field 'F' to control box 'F'
Brown/ White Ammeter to control box. Ammeter to main alternator terminal
Brown/ Yellow Alternator to 'no charge' warning light
Brown/ Black Alternator battery sensing lead
Brown/ Slate Starter relay contact to starter solenoid
Brown/ Orange Fuel shut-off (diesel stop)
Green Accessories fused via ignition switch
Green/Brown Switch to reverse lamp
Green/ Blue Water temperature gauge to temperature unit
Green/ Red Direction indicator switch to left-hand flasher lamps
Green/ Purple Stop lamp switch to stop lamps, or stop lamp switch to lamp failure unit
Green/ Light green
Hazard flasher unit to hazard pilot lamp or lamp failure unit to stop lamp
Green/ White Direction indicator switch to right hand flasher lamps
Green/ Yellow Heater motor to switch single speed (or to 'slow' on two- or three-speed motor)
Green/ Black Fuel gauge to fuel tank unit or changeover switch or voltage stabilizer to tank units
Green/ Pink Fuse to flasher unit
Green/ Slate a) Heater motor to switch ('fast' on two- or three-speed motor)
b) Coolant level unit to warning light
Green/ Orange Low fuel level switch to warning light
Light green Instrument voltage stabilizer to instruments
Light green/ Brown Flasher switch to flasher unit
Light green/ Blue a) Flasher switch to left-hand flasher warning light
b) Coolant level sensor to control unit
c) Test switch to coolant level control unit
Light green/ Red
Fuel tank changeover switch to right-hand tank unit or
entry and exit door closed switch to door actuator
Light green/ Purple Flasher unit to flasher warning light
Light green/ Green
Start inhibitor relay to change speed switch; or switch
to heater blower motor second speed on three-speed unit
Light green/ White Low air pressure switch to buzzer and warning light
Flasher switch to right-hand warning light; or
Light green/ Yellow differential lock switch to differential lock warning light
Light green /Black Front screen jet switch to screen jet motor
Light green /Slate Fuel tank changeover switch to left-hand tank unit; or entry and exit door open switch to door actuator
Light green/ Orange
Rear window wash switch to wash pump; or cab lock-down switch to warning
Orange Wiper circuits fused via ignition switch
Orange/ Blue Switch to front screen wiper motor first speed timer or intermittent unit
Orange/ Green Switch to front screen wiper motor second speed
Orange/ Black Switch to front screen wiper motor parking circuit, timer or intermittent unit
Orange/ Purple Timer or intermittent unit to motor parking circuit
Orange/ White Timer or intermittent unit to motor parking circuit
Orange/ Yellow Switch to headlamp or rear window wiper motor feed, timer or relay coil
Orange/Light green Switch to headlamp or rear window wiper motor parking circuit timer or relay coil
Orange/ Pink Timer or relay to headlamp or rear window wiper motor feed
Orange/ Slate Timer or relay to headlamp or rear window wiper motor parking circuit
Purple Accessories fed direct from battery via fuse
Purple/ Brown Horn fuse to horn relay when horn is fused separately
Purple/ Blue Fuse to heated rear window relay or switch and warning light
Purple/ Red Switches to map light, under bonnet light, glove box light and boot lamp when fed direct from battery fuse
Purple/ Green Fuse to hazard flasher
Purple/ Light green Fuse to relay for screen demist
Purple/ White Interior lights to switch (subsidiary circuit door safety lights to switch)
Purple/ Yellow Horn to horn relay
Purple/ Black Horn to horn relay to horn push
Purple/ Pink Rear heated window to switch or relay
Purple/ Slate Aerial lift motor to switch up
Purple/ Orange Aerial lift motor to switch down
Red Main feed to all circuits mastered by sidelamp switch
Red/ Brown Rear fog guard switch to lamps
Red/ Blue Front fog lamp fuse to fog lamp switch
Red/ Purple Switches to map light, under bonnet light, glove box light and boot lamp when sidelamp circuit fed
Red/ Green Bulb failure unit to right-hand-side and rear lamps
Red/ White 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
Red / Yellow Fog lamp switch to fog lamp or front fog fuse to fog lamps
Red/ Black Left-hand, sidelamp fuse to side and tail lamps and number plate illumination
Red/ Pink Sidelamp fuse to lighting relay
Red/ Slate Lamp failure unit to left-hand side and tail lamps
Red/ Orange Fusebox to rear fog guard switch
Red/ Slate Window lift main lead
White 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
White/ Blue switch to warning light, or electronic ignition distributor to drive resistor. Starter switch to starter solenoid or inhibitor switch
White/ Red or starter relay or ignition (start position) to bulb failure unit
White/ Purple Fuel pump no 1 or right-hand to changeover switch
White/ Green Fuel pump no 2 or left-hand to changeover switch. Start switch to starter interlock or oil pressure switch
White/ Light green to fuel pump or start inhibitor switch to starter relay or solenoid
White/ Yellow Ballast resistor to coil or starter solenoid to coil. Ignition coil contact breaker to distributor contact
White/ Black breaker, or distributor side of coil to voltage impulse tachometer
White/ Pink Ignition switch to radio fuse
White/ Slate Current tachometer to ignition coil
White/ Orange Hazard warning lead to switch
White/Yellow (or just plain yellow) a) Overdrive b) Petrol injection c) Door locks d) Gear selector switch to start
Yellow (or yellow/white) a) Overdrive b) Petrol injection c) Door locks d) Gear selector switch to start
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...
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