Ottawa MG Club

Lucas used colours in their wiring to tell us a story. Plain solid colours like red, white, brown, black, purple, green and blue tell you which circuit they belong to:

Black (B) is ground

Brown (N) is hot, but not fused.

Purple (P) is always hot, but is fused.

White (W) is hot when the ignition is on, but not fused.

Green (G) is hot with the ignition on, but is fused.

Blue (U) is the Headlight main feed, not fused.

Red (R) Parking /tail lights, not fused.

These colours sometimes have a second colour running through them, known as a tracer:

Blue/white - blue belongs to the headlight circuit, the tracer is for the high beam part of the circuit.

Blue/red - is for the headlights, but the tracer is to say it is for the low beams.

Red/white - is for the parking/tail lights. The white tracer says it is for the panel lights.

White/black - is for the ignition, the tracer says it is from the distributor.

Green/yellow - is hot with the ignition on, the yellow is to say it is for the right direction signal.

Green/blue - indicates it is for the left direction signal.

Purple/black - is hot and fused. The black tracer says it is for the horn button (on later cars).

Green/black - green is hot and fused with ignition on, the black says it is for the fuel gauge.