Automotive Wire Gauge Chart

Chassis amps ≠ NEC amps

Below 14 AWG the NEC building-wire table doesn't exist, so vehicle harness designers use free-air ratings from aerospace/marine references — the †-marked column in the table. These assume a single loose wire in moving air. A taped harness of 20 wires derates hard; use the value as a ceiling, never a target.

Where each size lives in a vehicle

• 20–16 AWG: sensors, memory feeds, dash illumination, speaker leads in the dash.
• 14–12 AWG: headlight/feed circuits, window and lock motors, radio main power.
• 10–8 AWG: charging feeds for dual battery systems, amplifier main runs (30–60 A).
• 4–1/0 AWG: starter alteration charges, big inverter inputs, welding leads on trucks.

Stranded-only, temperature-rated

Vehicle harness wire is always multi-strand copper, sized by cross-section in mm² by international OEMs; SAE gauge is the US equivalent. Engine bay sections must carry 125 °C (TXL) ratings; interior panels can use 85 °C (GXL). If you're replacing a burnt harness section, match insulation temperature first — the melt-trace on a harness fire tells you whether the last installer didn't.

Automotive wire gauge chart, load by load

The working picks, load by load, read like a service manual: memory keep-alive 20 AWG fused at 1–3 A; projection/in-car sensors 20-18 AWG; lighting, relays and small pumps 18-16 AWG; headlights and horn 14-12 AWG; alternator feeds 10-8 AWG sized to the alternator's rated output, not the nameplate peak; power amplifiers 8-4 AWG with the fuse sized to the wire, always near the battery; winches 2-0 AWG and short — nothing in a 12 V system rivals the current of a stalled motor. Those picks assume the resistance column above and a healthy 3%-of-system drop budget; doubling the length doubles the drop, which is why "run-it-short" is the first rule of any 12V DC wire gauge chart.

Insulation classes: GXL, TXL, SXL and friends

Insulation, not copper, makes automotive wire its own species. GXL (thin wall, 125 °C) is the modern engine-bay default; TXL sacrifices a touch of robustness for the thinnest wall — brilliant in tight harnesses that live behind dashboards; SXL is the thick-wall branch for exposed runs along the frame. Household THHN has none of those certifications: it cracks at flex joints, degrades hot, and leads to brittle fails in any stranded-class harness that actually moves. Pick the jacket by temperature zone — boot bay TXL/GXL, dashboard TXL, undercarriage SXL — not by color.

Grounding, fusing and the relay trick

Three habits separate a clean 12 V build from a flaky one. Fuse near the source: every positive run that leaves the battery deserves its fuse within arm's reach of the post — an unfused feed is a bare wire waiting for a crash. Ground at the load: a radiator fan grounded at the battery may run better than one grounded at a rusty fender stud, because the return path counts in the resistance budget too. Relay the real loads: a headlight switch is a signal, not a power path — size the switch leg small and let the relay carry the amps, then the harness diagram matches what an auto-parts counter sells. And whenever a harness crossing needs a physical reference, the circles on the actual size wire gauge chart print exactly the outside diameters that jumper kits come in.