Draw a car wiring harness, and get the parts list out of it

What you place on it

Ten kinds of component, each carrying its own pins, part number and notes: connectors, ECUs, relays, fuses, grounds, splices, switches, sensors, batteries and busbars. Pins are yours to name — an ECU pin called A3 IGN 2 is more use six months later than Pin 3 — and any component can be rotated in ninety-degree steps so the drawing matches the way the loom lies in the car.

A pin you have deliberately left empty can be capped, which marks it as blanked rather than forgotten. A component or a wire can be marked as a ghost: drawn faintly, present in the diagram, left out of the parts count. That is how you show the alternator you have not bought yet without it turning up on the order.

Wires that carry what a wire carries

Every wire has a colour, a second colour for stripes and splits, a gauge in AWG or mm², and a label. Twenty colours, because a factory loom does not limit itself to six, and both gauge scales because the connector is specified in one and the wire is sold in the other.

Drag a wire and it takes a bend point; wires route in straight legs rather than curves, which is what a wiring diagram looks like. A pair can be marked as twisted — CAN high and low drawn as the twisted pair they have to be.

What comes out

• The diagram, as PNG or JPEG, at a resolution that stays readable when it is printed and taped to the bench.
• A bill of materials, as CSV: every component grouped by type, part number and pin count, with quantities, so it goes straight into an order.
• A wiring table, as CSV: every wire with both ends, its colour and its gauge — the list you tick off while you crimp.

The project itself saves as a .harness.json file you keep. It also autosaves to this browser as you work, so closing the tab does not cost you the afternoon, and a file saved by an older version that has since developed a fault is repaired on load rather than refused.

What it is not

It does not check your electrical design. It will happily let you run a fuel pump off a 22AWG wire, earth a sensor to a signal pin, or wire a relay coil to nothing. It draws what you tell it and counts what you drew — the thinking is still yours.

It is also not a schematic capture tool. There is no netlist, no simulation and no PCB behind it. It is for the loom in a car, which is a different job with different mistakes.