For most 12V applications—like 4WD dual-battery setups, caravans, and boats—the industry standard is to use and Black for Negative .
While Red and Black are the baseline, more complex installations use additional colours to prevent "spaghetti" confusion: 12 Volt Wiring Colour Codes Australia
Ignition-switched power (only active when the key is on). Black: Chassis ground or negative return. 12 Volt Wiring Colour Codes Australia
Sometimes substituted for Red in specialized marine or solar applications to indicate a Live Charging Source . 12 Volt Wiring Colour Codes Australia
A red positive wire without a fuse within 40mm of the battery terminal is a fire hazard. The colour does not protect against overcurrent. Always size the fuse to the wire’s current rating.