Printable 12V outlet safety checklist

• Know the two formulas: watts = volts × amps (10 A at 12 V = 120 W) and continuous load ≤ 80% of the fuse rating.
• A 15 A dash fuse means 12 A of safe continuous load — about 144 W at 12 V. That is the ceiling for the whole circuit.
• Add up everything on that circuit before plugging in. Two 60 W devices are fine; a 60 W cooler plus a 100 W gadget is not.
• Engine running, voltage sits near 14.4 V, so wattage headroom rises a little — but plan for 12 V engine-off, the hard case.

The longer version of this math lives in our truck 12V power guide.

• Phone and tablet chargers — 10–20 W.
• LED cab lights and strips — 5–10 W.
• 12V cab fan — 10–15 W.
• Dash cam — 5–10 W.
• Compressor fridge — 45–60 W peak, well inside the ceiling.
• 12V heated blanket — 45–55 W, fine on its own circuit.

• Electric kettle — ~1,000 W. Nearly seven times the ceiling.
• Microwave or plug-in cooker — 800–1,200 W. Inverter and direct battery wiring only.
• Space heater — never on the dash socket. See why a space heater does not belong on an inverter either.
• Hair dryer or heat gun — same heating-element math, same answer.
• Any thermoelectric cooler with a loose, hot, or discoloured plug — driver reports of melted plugs are real; pull it and inspect.

• Keep the factory cable. If you must extend a cooler lead, use 14 AWG or thicker for runs under 3 m.
• Thin wire + long run = voltage drop and heat. A struggling compressor draws more amps to compensate.
• Never run cable coiled — a coiled extension is a heater. Lay it out or shorten it.
• Route cable where it cannot be pinched by the seat track, door, or bunk hinge.

• Touch-test plugs and sockets after 30 minutes on a new setup. Warm is fine; hot or soft plastic means unplug now.
• The fuse protects the wire, not your gear — never upsize a fuse to stop it blowing. It is blowing because something is wrong.
• With the engine off, unplug anything high-draw. A dead battery at 3 a.m. is a tow call, not a nap.
• Splitters multiply risk, not capacity. The fuse limit is for the circuit, not per socket.
• Smell hot plastic or see brown discoloration on the outlet? Park the device, replace the socket before the next trip.

For the full walkthrough behind these checks, read 12V outlet safety: what you can actually run.

Figures assume a 12 V system and standard 15 A dash circuits — check your owner’s manual; some trucks run 10 A or 20 A circuits.