Wire Harness Assembly
Also: wire harness, wiring harness, cable assembly, cable harness, wire harness manufacturing, custom cable assemblies, wiring loom, harness assembly, IPC/WHMA-A-620, cable and harness assembly
Wire harness assembly cuts, strips, crimps and terminates wire, then bundles it into harnesses and cable assemblies built and tested to IPC/WHMA-A-620.
617 shops tagged Wire harness among 843 electronics manufacturing companies in the Noramark directory
Wire Harness Assembly shops by state
A harness is a set of wires and cables cut to length, terminated and bound together so that it installs as one part. Wire is measured, cut and stripped, usually on an automatic machine that can also crimp a terminal on each end and print an identifier on the insulation. A crimp compresses the terminal barrel around the conductor strands into a gas-tight joint, and a second crimp grips the insulation for strain relief. Crimped contacts are pushed into connector housings until they lock, splices and solder joints are made and sealed with heat-shrink tubing, and the wires are laid out on a full-scale formboard whose pegs and fixtures set every branch length. The bundle is then tied, taped or sleeved, labeled and tested.
The trade distinguishes a cable assembly, typically one cable with a connector on each end and often an overmolded strain relief, from a wire harness, which has many wires and breakouts to several connectors. Machines do the cutting, stripping and crimping, but layout, insertion, routing and tying are still done by hand. That makes harnesses labor intensive, and it makes documentation, tooling and operator training the main quality controls.
The workmanship standard is IPC/WHMA-A-620, Requirements and Acceptance for Cable and Wire Harness Assemblies, with the same three product classes as the other IPC standards: Class 1 general, Class 2 dedicated service and Class 3 high performance. It gives criteria for strip length and strand damage, crimp shape, insulation support, solder joints, ties and markings. Crimp quality is controlled by using the terminal maker's applicator or hand tool, checking crimp height with a crimp micrometer against the terminal specification, and pull testing samples. Finished harnesses are tested for continuity and shorts on a tester that checks every circuit against the wire list, with high-voltage (hipot) and insulation-resistance tests where specified.
A harness is defined by its documents: a wire list (a from-to table) with gauge, color, length and terminations, a bill of materials with exact connector, terminal and seal part numbers, and a layout drawing with branch lengths and tolerances. Connectors and terminals are designed as a system, so a terminal must match the wire gauge, the insulation diameter and the housing, and must be crimped with the tooling its manufacturer specifies.
At a glance
| Typical tolerances | Length is the main dimension. Finished branch lengths are commonly toleranced at about ±6 mm (±0.25") on short leads up to 300 mm (12"), growing to ±13-25 mm (±0.5-1") or a percentage of length on long runs; tighter tolerances need fixtures and cost more. Defaults differ between shops, and where the drawing gives no tolerance the default table in IPC/WHMA-A-620 applies, so state a tolerance for each length. Strip length is held to about ±0.5-1 mm (±0.02-0.04"). Crimp height is held to the terminal manufacturer's specification, typically ±0.03-0.05 mm (±0.001-0.002"), and verified with a crimp micrometer and pull tests. |
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| Size limits | Wire from about 30 AWG (0.05 mm²) signal wire to 4/0 AWG (107 mm²) battery and power cable. Automatic cut-strip-crimp machines commonly cover about 26 to 10 AWG, with bench presses, hydraulic crimpers and hand tools for smaller and larger sizes. Harnesses range from a two-wire jumper to assemblies with hundreds of circuits several meters long; formboards of 1.2 x 2.4 m (4 x 8 ft) are typical and are joined end to end for long machine, vehicle and aircraft harnesses. Quantities run from one prototype to tens of thousands a year; high-volume automotive harnesses are a separate, largely offshore industry. |
| Surface finish | A finished harness is judged on workmanship and identification, not surface finish. Bundles are secured with cable ties, lacing or tape at set intervals and protected with braided sleeving, convoluted conduit, spiral wrap or heat-shrink tubing where they pass edges or heat. Wires are identified by insulation color, printed legends or marker sleeves, and connectors and branches carry labels. Sealed connectors use individual wire seals and cavity plugs; breakouts can be sealed with adhesive-lined heat-shrink boots or overmolding. Terminal plating (tin, silver or gold) should match the mating contact. |
| Lead time | Prototypes and first articles in 1-3 weeks when the connectors and terminals are in stock; production lots in 3-6 weeks. Connector, terminal and special-cable lead times set the schedule and run from days to several months, and crimp tooling for a terminal the shop has not run before can add weeks. A formboard and a test fixture are built once per part number. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Conductors are stranded copper, bare or tin plated, with silver or nickel plating on high-temperature and aerospace wire; solid wire is rarely used in harnesses because it fatigues when flexed. Insulation is chosen by temperature, voltage and environment: PVC for general appliance and equipment wire (UL 1007 and UL 1015 styles), cross-linked polyethylene for vehicles (SAE J1128 types such as TXL, GXL and SXL), PTFE and ETFE for aerospace and high-temperature wire (the SAE AS22759 family), and silicone for flexibility and heat. Multi-conductor, shielded, coaxial and twisted-pair cable are processed the same way, with extra steps for the shield. Terminals are brass, phosphor bronze or copper, tin plated for general use and gold plated for low-level signals. Protection comes from PVC and cloth tape, nylon cable ties, expandable braided sleeving, convoluted conduit, heat-shrink tubing and overmolded strain reliefs.
What drives the cost
- Labor: the number of circuits, terminations, splices and breakouts, and how much of the work is done by hand
- Components: connectors, terminals, seals and wire are a large share of the price, and minimum buy quantities weigh on small lots
- Tooling: crimp applicators or hand tools for each terminal, the formboard and the test fixture
- Wire and cable type: shielded, coaxial, high-temperature and large-gauge cable take more preparation
- Protection and sealing: braid, conduit, heat-shrink boots, overmolding and potting
- Testing and documentation: 100% continuity test, hipot, pull-test records, first article, IPC class, UL or traceability requirements
- Lot size: setup and kitting are spread over the lot
When to use it
- Wiring for machines, vehicles, appliances, control panels, medical devices and industrial equipment
- Replacing loose point-to-point wiring with one tested, labeled part that installs quickly
- Cable assemblies: power cords, signal and data cables, battery cables and sensor leads
- Products that need documented workmanship to IPC/WHMA-A-620 Class 2 or Class 3
- Prototype through mid-volume production, where a domestic shop can turn design changes quickly
When not to
- Standard cables (USB, Ethernet, power cords, common jumpers) that a catalog already sells
- Interconnects inside a compact product, where a flex circuit or board-to-board connectors save space and assembly labor
- Designs that still lack pinouts, connector part numbers and lengths: finish the documentation first, or pay the shop to engineer it
- Very high volumes of a stable design, where automated or offshore production is priced lower
Design tips
- Provide a wire list with from-to pin assignments, gauge, color, wire type and length, plus a layout drawing with branch lengths and a tolerance on each.
- Give manufacturer part numbers for connectors, terminals, seals and backshells, and name approved alternates; a terminal must match both the wire gauge and the insulation diameter.
- Use common wire gauges and as few terminal families as possible; each new terminal needs its own crimp tooling.
- Leave service length and respect the cable manufacturer's minimum bend radius; a common rule of thumb is about ten times the outside diameter.
- Stagger splices and keep them out of flex zones; show where the harness is clamped and where it must flex.
- Specify sleeving, strain relief and labels where the harness needs them, not everywhere.
- State the IPC/WHMA-A-620 class, the electrical tests (continuity, hipot, insulation resistance) and any UL, RoHS or traceability requirements.
- Send a sample or a 3D routing model when the harness replaces an existing one, and fit a first article before releasing production.
Frequently asked questions
- What is the difference between a wire harness and a cable assembly?
- A cable assembly is usually one cable, often jacketed and sometimes shielded, with a connector on each end. A wire harness bundles many individual wires and cables with breakouts to several connectors, bound with ties, tape or sleeving so it installs as one part. Shops that build one generally build the other, and the same workmanship standard, IPC/WHMA-A-620, covers both.
- What is IPC/WHMA-A-620?
- The industry workmanship standard for cable and wire harness assemblies, published jointly by IPC and the Wiring Harness Manufacturer's Association. It gives acceptance criteria for wire preparation, crimped and soldered terminations, connectors, splices, marking, securing, shielding and testing, in three product classes. Class 2 suits most industrial and commercial equipment; Class 3 is for high-reliability products such as medical, aerospace and defense.
- How are crimps tested?
- Three ways. Crimp height is measured with a crimp micrometer and compared with the terminal manufacturer's specification. Sample crimps are pull tested to a minimum force for the wire gauge. For validation, a cross-section shows whether the strands are fully compressed without voids. Production presses often add crimp force monitors that flag a bad crimp as it is made.
- What do I need to send for a wire harness quote?
- A drawing or wire list with every circuit (from, to, gauge, color, wire type), connector and terminal part numbers, branch lengths with tolerances, any sleeving, labels and sealing, the test requirements, the IPC class and the quantities. A sample harness helps when drawings are incomplete, but the shop will still need the connector part numbers.
- Should harness terminations be crimped or soldered?
- Crimped, for nearly all harness terminations. A crimp made with the right tooling is fast, repeatable and holds up under vibration, while solder wicks up the strands and leaves a stiff point where the wire can fatigue. Solder is used where the connector is designed for it, such as solder-cup contacts and some shield terminations, and the joint is then supported with heat-shrink tubing.
