Dark editor window titled F150 showing a wiring layout: several harness trunks with branches to connectors spread around the canvas, and dozens of curved wires converging on a column of plugs in the centre

Desktop appSolo designer and engineerDrawing 44 of 47

hexis
.harness

My own desktop app for designing wiring harnesses, offline on a Mac. It reads and writes the open .harness file format, and I'm using it to design the full harness for a 1985 F-150 with a Coyote V8 swap.

StatusWorking, version 0.1.0, 2026
Built withReact, TypeScript, Electron, React Flow
Runs onmacOS, offline
File formatthe open .harness format, read and write
Parts804 in an offline catalog, Deutsch, TE, Molex, JST, Aptiv
Examplea 1985 F-150 Coyote swap, 512 connections

Sheet 02 of 06/Why

A harness tool that stays offline

The goal was a harness editor that runs offline as a Mac app, with the files on my own disk. So I wrote my own, built around the open .harness file format.

Bar chart of the ten F-150 harnesses by number of connections, from 11 for the truck tie-in pigtails to 131 for dash and doors, with circuits and connectors listed beside each bar — *PL 01*Connections per harness, counted from the design's own wire list. Dash and doors is the biggest at 131.

Zoomed-out layout view showing several harness trunks with branches spread around the canvas and curved wires converging on a central group of plugs — *PL 05*The full layout at a glance: ten harnesses around the two controllers in the middle.

Sheet 03 of 06/Parts

Issued as separate drawings

I split this project into parts. Each part below has its own page, with its own sections and pictures.

Part 01 / 01
F-150 Coyote harness
The example: a full harness for a 1985 F-150 with a Coyote V8 swap. Ten harnesses, 512 connections, 266 circuits and a fuse box of my own.
8 sections →

Sheet 04 of 06/Views

Two views of one harness

The schematic view shows every pin and wire as a drawing. The layout view shows the same harness as physical bundles, with branches running out to each connector, so I can see where every wire actually goes.

Zoomed-out schematic of a large wiring diagram on a dark canvas, with groups of connector blocks joined by red, purple, green and grey wires — *PL 02*The schematic view of the whole truck, every connector and wire on one sheet, coloured by wire colour.

Close-up of the schematic showing connector blocks for fog lights, headlamps, horn and wiper motor, each listing numbered pins, signal names and a DT06 plug part — *PL 03*Close up in the schematic: each connector lists its pins, its signals and its plug, here the body controller's front lighting.

Layout view close-up with the injector and coil harness bundles at lower left and two columns of controller header connectors in the middle with wires fanning in — *PL 04*The layout view near the controllers: the injector and coil harnesses on the left, and every harness plug landing on the engine and body controller headers.

Sheet 05 of 06/Parts

Real parts

Connectors come from a built-in catalog of 804 parts that works offline: Deutsch, TE, Molex, JST and Aptiv plugs, plus contacts, cable, splices and coverings. Each part carries its own pinout.

Parts catalog dialog listing Deutsch pins, sockets and DT receptacles with gauge ranges and descriptions, and tabs for contacts, connectors, locks and cavity plugs — *PL 06*The built-in parts catalog: 804 parts that work offline, here Deutsch DT contacts and plugs with their wire gauges.

Sheet 06 of 06/Desktop

A real Mac app

It ships as a Mac app with autosave, undo and revisions. It counts a bill of materials straight from the drawing, builds a wiring table for every connector, and exports to PDF, CSV and Excel. It's covered by 47 test files, from unit tests up to end-to-end tests that click through the editor in a browser.

Bill of materials table listing diodes, splices, Deutsch contacts and ring terminals with part numbers, manufacturers, unit prices, quantities and totals — *PL 07*The bill of materials, counted straight from the drawing, with prices and a CSV export.

Wiring tables dialog with one table per connector, listing cavity numbers, signals, destinations, wire numbers and wire colours — *PL 08*Wiring tables for every connector: cavity, signal, destination, wire and colour, exportable to CSV or Excel.

hexis.harness