Lucas Wiring Colours

All Lucas wiring looms have a common colour code, whether the loom is in a Sprite, MG, Jaguar, Healey, Triumph etc etc. Knowing the code can help a lot, particularly when a manual isn't handy.

Some of the codes are are as follows.

Brown is main power live all the time from the battery, sometimes via the voltage regulator, to the fuse box where it powers all items independent of the ignition system (eg: horn). If you see a heavy brown wire, be careful as it will be live.

Brown with a blue trace is the power feed from the voltage regulator to the light switch (see below - blue = headlights). Brown with a green trace is the power feed from the fuse box to the horn. Brown with any colour trace is likely to be live all the time - be careful.

White is the wire from ignition switch. It will go to the coil and other items that need to be powered by turning on the ignition, such as ignition light and fuse box. The white wires are live only when the ignition is turned on.

Green is power out of the fuse box - the white wire referred to above takes power to the fuse, and the green wire takes power out of the same fuse. So the green wires are also live when the ignition is on, and they are delivering power to various items such as wiper motor, brake light switch, heater switch, fuel gauge, blinker can and tacho. So if your tacho dies and your blinkers don't work, try the wipers. If they don't work either, you just blew the fuse.

One of the above green wires delivers power to the blinker can, and power emerges from the can as green with brown trace and heads to the blinker switch. From there, it heads out as either green with red trace to the left hand blinkers, or green with white trace to the right hand blinkers.

So a plain green wire is powered by the ignition switch (via the fuse box) and green with any colour trace is coming off another switch (heater, brake light, wipers etc etc) or the fuel gauge.

There are so many items powered by green wires that it would be impractical to connect all these wires into the fuse box. As a result, often only one or two green wires come out of the fuse box, but behind the dashboard the bullet ends all get plugged together by one or more of those black rubber joiners. If some of the above mentioned items work and others don't, it's possible that there is a stray green wire behind the dash that hasn't been plugged into it's power supply rubber joiner.

Blue (heavy wire) is the power feed from the headlight switch to the dip switch. From there the power heads out via blue with red trace (low beam) or blue with white trace (high beam and warning light).

Red is always side lights or parking lights. A red wire also goes to the dash light switch, and comes out of the switch as red with white trace. Any red wire with white trace will be a power supply to a gauge illumination light.