Wiring diagram maker for cars
Car wiring diagram software that also tests the circuit
WireForge is an online editor for automotive wiring diagrams. Draw the circuit from real components, give every wire a colour, cross-section and length, then press Simulate and see whether it works — voltages, currents, blown fuses and overloaded wires — before you cut a single wire in the car.
Open the editor · ▶ Run the live demo
Draw a diagram the way a car is wired
- Power: battery, body ground, positive and negative distribution blocks, fuse box with up to 10 channels.
- Switching: switches and momentary buttons, 4-pin, 5-pin and dual-87 relays, blade fuses from 0.5 to 400 A.
- Loads: lamps and ready devices — headlights, fog and brake lights, horn, wiper and fan motors, starter, alternator, injectors, ignition coils.
- Sensors: crankshaft and camshaft position, throttle position, MAP, MAF, coolant and air temperature, oil pressure, lambda.
- Engine control units with connector pinouts, and your own blocks for anything else.
The parts library has what a 12 V or 24 V vehicle circuit is made of. Drag a part onto the canvas, connect its pins and the wire routes itself around other components. Pins are named the way they are on the car: relay terminals 30, 85, 86, 87, 87a, alternator B+ and D+, sensor +5V, SIG and GND.
Wires with real colours, sizes and lengths
Each wire carries the data the workshop needs: colour (red, black, brown, blue, green, yellow and more), cross-section in mm² or AWG, and length. The simulator uses the same numbers, so a long thin wire really loses voltage and a wire that is too thin for its fuse is flagged.
Check the circuit before you build it
A drawing can look right and still not work. In WireForge you switch the circuit on: flip a switch, hold a button, drag the engine speed. Relays pull in, lamps light up as bright as their real power, motors turn. Click any wire to read its current and voltage. Plain-language warnings point at a short circuit without a fuse, a relay with 30 and 87 swapped, a load without ground or a voltage drop over 0.5 V.
Hand it over as documentation
When the diagram is ready, export a PDF pack with the schematic, a bill of materials and a wire list — colour, size, length, from and to — for the workshop or the customer (Pro). Every change is saved with version history, and a project can be private, shared by link or published in the gallery.
Make your first diagram in five minutes
- Open the editor — no account needed to try it.
- Drag a Battery, a Fuse, a Switch and a Lamp from the library, and a Ground.
- Connect battery + → fuse → switch → lamp + and lamp − → ground.
- Press Simulate and click the switch: the lamp lights and the wires show their current.
- Register for free to save the project to your account.
Questions
Is there a free car wiring diagram program?
Yes. WireForge has a free plan with the full editor and simulator; you can try the editor without registering at all.
Do I need to install anything?
No. WireForge runs in the browser on Windows, macOS, Linux or a Chromebook; projects are saved to your account.
Can I draw 24 V truck circuits?
Yes. Batteries, lamps, relay coils and devices take any voltage from 6 to 48 V, so 12 V cars, 24 V trucks and buses all work.
Can I print the diagram or share it?
You can share a project by link or publish it in the public gallery. Pro adds a PDF pack with the schematic, bill of materials and wire list.
More guides
- Automotive circuit simulator
- Relay wiring diagram
- Fuse and wire size calculator
- Starter and alternator wiring
- ECU wiring diagram
- Radiator fan relay wiring
- LED light bar wiring
- Fog light wiring
- Horn relay wiring
- Voltage drop calculator
- How to find a short circuit
- Automotive wire gauge chart
- 12 V vs 24 V wiring
- Fuse box wiring
- Blade fuse ratings and blow time
- Ignition coil wiring
- Fuel injector wiring
- Crankshaft sensor wiring
- Battery warning light on