Winch · 12 V · heavy cables
Winch wiring diagram: battery cables, fuse and isolator
A 12 V winch is the biggest current in the vehicle: 150–200 A on a medium pull and up to 400 A near its limit. It runs only for short bursts, so its wiring follows its own rules: very thick, very short cables, protection at the battery, and a switch to make it dead when not in use.
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The circuit
- Battery + → fuse or circuit breaker (250–400 A, per the winch maker) → isolator switch → contactor (solenoid pack) → motor.
- Motor − → battery − with a cable as thick as the + cable, not just through the chassis.
- The remote only switches the contactor’s coils (a few amps on a thin fused wire); the contactor carries the motor current and reverses it for In and Out.
- Cables of 35–50 mm² are typical; follow the winch maker’s size for your cable length.
Why the usual wire tables do not fit
Wire ratings in tables are for continuous current. A winch pulls 200 A for a minute and then rests, so a 50 mm² cable carrying more than its continuous rating is normal here — the simulator flags it as overloaded on a long pull, and that is exactly the reason to respect the winch’s duty cycle. What matters as much is voltage: at 160 A the battery sags towards 10 V, so keep the engine running so the alternator helps.
See also: Inverter to car battery · Automotive wire gauge chart
Pull in the simulator
- Run the live demo: a 250 A fuse at the battery, an isolator, the Pull contactor and the winch motor on 50 mm² cables.
- Switch the isolator on and hold Pull: the motor draws about 160 A.
- Look at the motor voltage: the battery sags to under 10 V — the simulator warns about low voltage.
Questions
Does a winch need a fuse?
Many kits are sold without one, but a breaker or fuse at the battery protects the long + cable from a short in an accident. Use one rated for the winch’s maximum current.
Why an isolator switch?
A stuck contactor or a damaged remote can run the winch on its own. The isolator makes the cable dead whenever the winch is not in use.
Can I run the winch with the engine off?
Only briefly. Under load the battery voltage drops fast and the winch slows; the engine running keeps the voltage up.
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