Car wiring guides
How car circuits are wired, explained with live diagrams you can switch on: relays, fuses and wire sizes, starting and charging, ECUs.
Car wiring diagram software
Draw car wiring diagrams in the browser: batteries, fuses, relays, switches, lamps, ECUs and sensors. Simulate the circuit and export a wire list. Free plan.
Automotive circuit simulator
Simulate car electrical circuits online: voltage and current on every wire, voltage drop, relays, fuses blowing on a real time-current curve, wires and bulbs burning out.
Relay wiring diagram
How to wire a 12 V car relay: what terminals 30, 85, 86, 87 and 87a do, 4-pin and 5-pin wiring diagrams, where the fuse goes and common mistakes — with a live simulation.
Fuse and wire size calculator
Enter the load power and wire length to get the current, the blade fuse rating and the wire cross-section (mm² and AWG) with voltage drop for a 12 V or 24 V car circuit.
Starter and alternator wiring
How a car’s starting and charging circuit is wired: ignition switch, starter relay and solenoid, alternator B+ and D+, the charge warning lamp — with a live simulation.
ECU wiring diagram
How to wire an engine ECU: main relay, power and ground pins, 5 V sensor supply, crank sensor, injectors and ignition coils. Simulate it with ECUMASTER EMU presets.
Radiator fan relay wiring
How to wire an electric radiator cooling fan through a relay: thermoswitch or ECU control, fuse and wire size for a 15–25 A fan, and the mistakes that kill relays.
LED light bar wiring
How to wire an LED light bar on a car or 4x4: relay, switch, fuse and wire size for 120–300 W bars, and why the wire gets thicker on a long run.
Fog light wiring
How to wire front fog lights: relay, switch, fuse and wire size for two 55 W lamps, the parking-light interlock, and what happens when a fog lamp wire chafes.
Horn relay wiring
How a car horn is wired: horn relay, the steering-wheel button that switches to ground, fuse and wire size for one or two horns, and why a horn clicks but does not sound.
Voltage drop calculator
Calculate the voltage drop on a car wire from current, length and cross-section, see why lamps get dim and motors slow, and find the wire size that keeps the drop under 3 %.
How to find a short circuit
A fuse keeps blowing? How to find a short to ground in car wiring: narrow down the circuit, the test-lamp-in-place-of-the-fuse trick, and where wires usually chafe.
Automotive wire gauge chart
Car wire size chart: cross-section in mm² and AWG, the current each one carries in a harness, the largest fuse it can take, and resistance per metre for voltage drop.
12 V vs 24 V wiring
How 24 V truck and bus wiring differs from 12 V car wiring: two batteries in series, half the current, thinner wires, and why a 12 V lamp on 24 V burns out at once.
Fuse box wiring
How to wire an auxiliary fuse box and power distribution in a car or project vehicle: main fuse, fused channels, positive and negative bus bars, and ground points.
Blade fuse ratings and blow time
How automotive blade fuses work: colour codes from 2 to 30 A, how long a fuse takes to blow at 135 %, 2× and on a short, and how to choose the rating.
Ignition coil wiring
How to wire ignition coils to an ECU: terminals 15, 1 and 4 on a plain coil, +12V, IGT and GND on a coil with a built-in igniter, and the classic wiring mistake.
Fuel injector wiring
How fuel injectors are wired: +12 V from the main relay, the ECU switching each injector to ground, high and low impedance injectors, and how to check the circuit.
Crankshaft sensor wiring
How to wire a crankshaft position sensor to an ECU: two-wire inductive sensors with a shield, three-wire Hall sensors, polarity, and why there is no spark without it.
Battery warning light on
Why the battery or charge warning light comes on: how the lamp is wired to the alternator D+ terminal, what it means when it stays on, flickers or never lights.