Wiring Diagrams
Lucas Wiring Color-Code Quick Decoder (BS-AU7)
Use the filter box below to look up any Triumph/Lucas wire color or tracer (main color / stripe).
| Color Code | Circuit / Function |
| Brown (N) | Main battery feed (unfused, always hot) — starter solenoid, alternator/regulator, ignition switch |
| Brown / White (NW) | Ammeter / alternator warning & main feed to lighting switch |
| Brown / Blue (NU) | Alternator / control box to ignition switch & fuse box |
| White (W) | Ignition-switched unfused feed — coil, fuel pump, fuse box input |
| White / Red (WR) | Ignition switch (start) to starter solenoid |
| White / Black (WB) | Coil (negative / CB) to distributor contact breaker / tachometer |
| Green (G) | Ignition-switched fused circuits — gauges, wipers, turn signals, brake lights, heater |
| Green / Brown (GN) | Reverse lamp switch to reverse lamps |
| Green / Purple (GP) | Brake light switch to brake lamps |
| Green / Red (GR) | Left-hand turn signal indicators |
| Green / White (GW) | Right-hand turn signal indicators |
| Light Green / Brown (LGN) | Flasher unit to turn signal switch |
| Light Green / Green (LGG) | Voltage stabilizer (10V) to fuel & temperature gauges |
| Blue (U) | Headlight switch to dipper (dimmer) switch |
| Blue / White (UW) | High beam headlights & main beam warning lamp |
| Blue / Red (UR) | Low (dipped) beam headlights |
| Red (R) | Side / parking lights, tail lights, license plate lamp, and dash illumination feed |
| Red / White (RW) | Instrument panel lights (via rheostat / dimmer) |
| Purple (P) | Fused always-hot accessories — horns, interior courtesy light, hazard flasher |
| Purple / Yellow (PY) | Horn push to horns |
| Black (B) | Ground / Earth return to chassis |
If you haven’t guessed, the Haynes manual’s wiring diagram is VERY wrong especially for US 1500’s. Tom O’Malley has spent many hours redesigning wiring schematics for maximum readability. They are the best diagrams I have ever seen saving me many hours troubleshooting. They are so good I wish I had thought of them. Tom, if you are out there, email us!
A 75 Spitfire, download this link. (1.1Mb)
A 76 Spitfire, download this link. (1.1Mb)
A 78-80 Spitfire (78-79.5 in the US), download this link. (1.1Mb)
Modified Tom O’Malley diagrams:
GT6 Mk III (non emissions), download this link.
Non-Tom O’Malley diagrams:
Spitfire MkIV wiring diagram from the factory manual.
A 1979.5-80 Spitfire (electric fan), download this link. Also the key to the diagram.
North American 948 Heralds, Spit Mk2 and Triumph 10(outside link), posted by Andrew Mace
Here is a SET of wiring diagrams for the Overdrive wiring in PDF format. Since many manuals show the diagrams differently or poorly I have shown all options from all manuals I could find.