A wire harness looks simple on a drawing: a few wires, some connectors, a length for each branch. That is exactly why harness quotations from Vietnam diverge. One factory prices genuine connectors and an applicator made for the terminal; another prices a compatible terminal and a bench press it already owns. Both harnesses pass a continuity test. Only one of them will still be making good contact after a few years of vibration.
This article covers what has to be settled before a Vietnamese harness maker starts cutting wire: the drawing and the bill of materials, the crimp specification, the workmanship standard, the tests, and how connectors and terminals reach the line.
💬 Have a harness drawing and need it quoted on the same basis by several Vietnamese factories? Send us the drawing and the BOM and we will check what is missing before it goes out.
What must the drawing and BOM fix before a factory quotes?
A harness drawing must fix every wire, every terminal and every connector by part number, plus lengths with tolerances, the pin-out and the protection materials, because anything left open is filled with the factory’s own default.
Harness makers build a full-scale formboard from your drawing. If the drawing is missing a line, the board is built on a guess, and every harness off it repeats the guess. These items decide whether two quotations describe the same product:
| Item | What to state | What happens if it is left open |
|---|---|---|
| Wire | Conductor size, insulation material, temperature rating, colour, and the cable standard or wire style | A cheaper wire with a lower temperature rating is quoted |
| Terminals | Maker and part number for each, plus plating | A “compatible” terminal that may not mate reliably with your connector |
| Connector housings | Maker and part number, including any secondary lock or seal | Wrong lock or seal variant; water ingress or a pin that backs out |
| Pin-out | A wiring table, from-to by circuit, with connector views stated as mating face or wire side | Mirrored pin-outs, the classic first-article failure |
| Lengths | Branch lengths, the point each length is measured from, and the tolerance | Each factory measures to a different point |
| Protection | Tape type and wrap style, conduit, sleeving, heat shrink, grommets, clips | Protection that looks the same but fails heat or abrasion |
| Labels and marking | Label content, position, material and print method | Unreadable labels after assembly or cleaning |
| Workmanship class | The standard and class that sets acceptance | Disputes about whether a crimp or splice is a defect |
| Tests | What is tested on every harness, and the limits | ”Tested” means a continuity check only |
Two points cause more rework than any other. First, state whether connector views are drawn from the mating face or from the wire side; a mirrored view produces a harness that is wired perfectly to the wrong pins. Second, give each length a reference point, such as the connector face or the centre of a branch point, rather than “overall length”.
Machined and moulded parts that go into the same product follow their own drawing rules; for those, see fixing the drawing before a Vietnamese machine shop quotes.
Terminals and crimping: whose specification governs?
The terminal maker’s application specification governs the crimp — crimp height, bellmouth, conductor brush and insulation grip — and the purchase order should say so, together with the tooling the factory will use to achieve it.
A crimp is a cold-formed joint. Its quality depends on the terminal, the wire and the tool together, which is why terminal makers publish application specifications for each terminal and wire range. The checks that follow from that specification are well established:
- Crimp height. Measured on the first piece of every setup, and at intervals during the run, against the terminal maker’s value for that wire size.
- Pull-out force. A destructive test that confirms the conductor is held. The minimum value comes from the terminal specification or from the workmanship standard you name; write which one applies.
- Cross-section. A cut, polished and photographed crimp shows whether the strands are compressed evenly. Ask for it at first-article approval and after any change of applicator, terminal lot source or wire.
- Visual checks. Insulation inside the conductor crimp, strands outside the barrel, a missing bellmouth or a bent terminal are all visible defects with a defined accept or reject line in the workmanship standard.
Agree the tooling, not just the result
Ask each factory to state, per terminal, whether it will use an applicator designed for that terminal or a hand tool, and how it will prove the crimp height. Factories that produce harnesses in volume usually run automatic or semi-automatic cut-strip-crimp machines with applicators; low-volume work and repairs may be done by hand. Neither is wrong, but they cost differently and they are controlled differently, so the quotation should say which one is priced.
Require a crimp record for each setup: terminal, wire, applicator identifier, measured crimp height, pull test result and the operator. When a field failure comes back, that record is the difference between tracing it to one applicator and suspecting every harness ever shipped.
Which workmanship standard, and which class?
Name IPC/WHMA-A-620 and the class — 1, 2 or 3 — in the purchase order, state the revision, and say where your drawing overrides it; without that, there is no shared line between an acceptable and a rejectable harness.
IPC/WHMA-A-620 is the industry standard for cable and wire harness assemblies. IPC describes it as setting the materials, methods, tests and acceptability criteria for crimped, mechanically secured and soldered interconnections. Revision E, released in December 2022, aligned its soldering requirements with IPC J-STD-001. Standards catalogues list Revision F with an October 2025 publication date, so confirm the current revision before you write it into a contract.
The class reflects the product, not the price. Class 1 is general products where function is the main requirement; Class 2 is dedicated-service products where extended life matters; Class 3 is high-performance products where downtime cannot be tolerated. The standard leaves the choice of class to the user — you. If you do not choose, the factory will build to the class it normally builds to, and a later argument about a solder splice or a nick in the insulation has no answer.
Where an industry has its own requirements, put them on the drawing as well. One example worth checking: some road-vehicle drawings still cite ISO 6722-1 for single-core cable, but national standards catalogues list that edition as withdrawn, with the ISO 19642 series now covering the ground. A factory buying wire against an outdated reference is following your drawing, not making a mistake.
Checked against IPC’s release for Revision E, standards catalogue entries for Revision F and ISO 6722-1, on 19 October 2026.
💬 Not sure which class your harness should be built to, or whether your drawing cites a current cable standard? That review is part of how we run sourcing from Vietnam. Send us the drawing.
Which tests should every harness pass?
Continuity is the floor, not the test plan; decide which electrical, mechanical and visual checks apply to every harness, which apply per lot, and who owns the test board.
| Test | What it catches | Typical frequency to agree |
|---|---|---|
| Continuity and short circuit | Open circuits, wrong pin, shorts between circuits | Every harness |
| Insulation resistance or dielectric withstand (hipot) | Damaged insulation, contamination, pinched wires | Every harness, or per lot, depending on voltage and risk |
| Connector seating and lock | Terminals not fully locked, missing secondary locks | Every harness, often on the same test board |
| Dimensional check on the formboard | Branch lengths and positions out of tolerance | First piece per shift, then sampled |
| Crimp height and pull test | Poor crimps | Each setup and at set intervals |
| Crimp cross-section | Uneven compression, missing strands | First article and after changes |
| Visual inspection to the named class | Damaged insulation, wrong tape, poor splices, label errors | Every harness |
The test board — the fixture the harness plugs into for the electrical test — is usually built by the factory for your harness. Decide at the quotation stage who pays for it, who owns it, and what happens to it if production moves. The same logic applies to formboards. The ownership clauses that protect moulds also work for test fixtures; see mould and tooling ownership in Vietnam.
Ask that the test program checks connector seating, not only electrical paths. A terminal that is electrically connected but not locked will pass a continuity test on the bench and back out in service.
Supplying connectors, or letting the factory buy them
Whether you consign connectors and terminals or let the factory buy them, require traceable sources and write down who carries shortage and leftover stock — and ask early how the factory is set up for customs, because that decides how consigned parts enter.
Connector housings and terminals are designed to work as a system. Buyers often consign the critical ones, or require the factory to buy them from the maker’s authorised distribution, because a terminal that is dimensionally similar but from another source may not hold contact force over time.
| Arrangement | When buyers choose it | What to write down |
|---|---|---|
| Factory buys everything | Standard parts, stable demand | An approved list of makers and part numbers per line, a ban on unapproved substitutes, and authorised sourcing only |
| You consign critical parts | Connectors under allocation, specified seals, customer-mandated parts | Receiving inspection, an allowance for setup losses, storage, stock reports and the return of surplus |
| Mixed | Most programmes | A line-by-line list showing who supplies what |
Consigned parts also change the legal shape of the order. When you supply material and pay for the work, Vietnamese law treats the arrangement as processing rather than a plain purchase; that distinction and its customs consequences are set out in contract manufacturing in Vietnam, step by step.
Many harness makers sit in industrial zones and some operate as export processing enterprises. Under Article 26(4) of Decree 35/2022/ND-CP, as Vietnam Customs restated it in August 2026, goods exchanged between an export processing enterprise and other areas of Vietnam that are not non-tariff zones are treated as exports and imports, with listed exceptions. In practice, that affects how a consigned part bought from a Vietnamese distributor reaches such a factory, so ask the factory and its customs agent to describe the route before your first shipment. Checked against the Ministry of Finance’s published report of the Customs Department’s guidance on 19 October 2026; confirm against the current text for your case.
For how to control alternate parts and change notices once production runs, the method in electronics contract manufacturing in Malaysia applies equally to harness components.
From first article to the production lot
Approve the formboard and the first article together, keep a signed reference harness on both sides, and treat any change of wire, terminal source, applicator or test program as a change that needs your approval.
A workable sequence:
- Drawing review. The factory returns questions in writing: unclear views, missing tolerances, parts it cannot buy. Answer them on a revised drawing, not in chat.
- Formboard and first article. The factory builds the board and the first harnesses. You receive the first-article report: dimensions, crimp heights, pull tests, cross-section photographs and the electrical test result.
- Reference harness. A signed harness is kept by each side as the visual reference for tape, routing and labels. The approval stages are described in sample approval before a Vietnamese production run.
- First production lot. Watch this lot most closely; it is where new operators and new setups first meet your design.
- Ongoing lots. A certificate of conformance to your drawing revision and class, the electrical test record and crimp records on file. For the final check before shipment, see pre-shipment inspection and AQL from Vietnam.
Each change should arrive as a numbered drawing revision with an effective date, and the factory should confirm which lot is the first one built to it.
💬 Want someone in Vietnam to run the first-article review and keep the crimp and test records straight? Tell us about the harness and the volumes.
Frequently asked questions
1. What do I need to send a Vietnamese factory to quote a wire harness?
A drawing with lengths, tolerances and reference points; a wiring table; a BOM with maker part numbers for wire, terminals, housings, seals and protection materials; the workmanship standard and class; the test requirements; and label and packing instructions. Expected volumes complete the picture.
2. Can the factory use compatible terminals instead of the ones on my BOM?
Only with your written approval. A compatible terminal may fit the housing but differ in contact force or plating. If you allow it, approve a named part number after a first-article check, and record which lots use it.
3. Is a continuity test enough?
Usually not. Continuity finds open circuits and wrong pins, but not damaged insulation, weak crimps or unlocked terminals. Add insulation or hipot testing where voltage or risk justifies it, crimp checks per setup, and a seating check on the test board.
4. Which IPC/WHMA-A-620 class should I choose?
The class follows the product’s use. Class 1 is for general products, Class 2 for dedicated-service products and Class 3 for high-performance products where failure cannot be tolerated. Choose it yourself and state the revision; otherwise the factory chooses.
5. Who should own the formboard and the test board?
Whoever pays for them, if the contract says so. Agree ownership, marking and return at the quotation stage, so that a second source or a move to another factory does not start with rebuilding the test equipment.
Sources: IPC, “IPC Releases IPC/WHMA-A-620E, Requirements and Acceptance for Cable and Wire Harness Assemblies” (22 December 2022); standards catalogue entries for IPC/WHMA-A-620F (October 2025) and ISO 6722-1:2011; Decree 35/2022/ND-CP, Article 26(4), as reported by Thời báo Tài chính Việt Nam on 23 August 2026. Checked on 19 October 2026.
More industrial sourcing guides: PCB Assembly in Vietnam: Data, Parts, Test and Ramp-Up · Jigs, Fixtures and Automation Machines Built in Vietnam · Thai Metal and Plastic Parts for Appliances and Machines. All guides by category are on the industrial sourcing page.