Using the correct wire colours makes your electrical system safe and easy to troubleshoot.
UK 12v Colour Code Standard
| Wire | Colour | Typical Use |
|---|---|---|
| Positive (main) | Red | Battery positive, DC-DC charger output |
| Negative | Black or white | Battery negative, return to ground |
| Fridge positive | Blue | 12v fridge power |
| Solar positive | Red (fused) | Solar panel to controller |
| USB/Yacht style | Brown | Positive on newer marine systems |
| Switched positive | Yellow | Via ignition switch or relay |
| Lighting | Grey or green | Ceiling and cupboard lights |
Best Practice
- Always label both ends of every wire with a label maker or tape
- Use red for positive, black for negative — do not deviate
- Use fuses at the battery end of every positive wire
- Use 16mm² (red/black) for main battery cables
- Use 2.5mm² for lights and small loads
- Use 6mm² for solar panels and fridge circuits
Common Mistakes
- Using black for both positive and negative (DANGEROUS)
- Not labelling wires (impossible to troubleshoot later)
- Using different colours for the same circuit (confusing)
What to Buy
A wire colour pack from 12v Planet or Vehicle Wiring Products. £20 for 10m each of red, black, blue, yellow, and white.
