Approving a custom wire harness manufacturer should not depend on a showroom tour, a certificate photograph or one passing sample. Buyers need evidence that the proposed site can control the specified materials, termination system, assembly route, test coverage and delivery configuration over repeated production.
This custom wire harness manufacturer audit checklist provides twenty weighted questions, a reusable finding record and decision rules. The scorecard is a proposed buyer tool, not a certification scheme. Agree on scope, criteria, sampling and approval thresholds before the audit, and keep supplier approval separate from product qualification and purchase authorization.
Establish the Audit Scope, Criteria and Evidence Trail
Identify the actual manufacturing route
Record the site, product family, proposed part revisions, volumes, outsourced operations and production processes covered. Determine whether terminals, molded parts, splices, overmolds or electronic subassemblies are purchased or manufactured on site. Audit the responsibility actually assigned to the supplier rather than assuming every process happens in its factory.
ISO 19011:2026 provides guidance for management-system audits, audit programmes and auditor competence. It is not a harness product specification, a test method or proof of supplier approval. Use the applicable customer documents and supplier obligations as the audit criteria; the following scorecard remains an original buyer-planning proposal.
Define a risk-based sample plan covering relevant variants, shifts, equipment, recent changes and complaint history. Record the population and actual number of records or products examined for each question. Small, selected samples cannot establish universal conformity; unexplored scope must be stated in the report.
Follow requirements into actual production
Trace a requirement through customer inputs, project planning, design/process risk, approval evidence and serial-production controls. Where required by the customer or contract, review applicable APQP, PPAP, core-tool and customer-specific records. Do not assume these requirements apply identically to every industrial or low-volume project.
Check the linked chain: Process Flow → PFMEA or approved risk review → Control Plan → Work Instruction → Inspection Record. The manufacturing process guide explains these operational gates. A document trail is credible only when the observed operation, materials and records agree with it.
Combine interviews with observation and record tracing. Ask an authorized operator to explain a reaction rule, then inspect an actual example of its use. Preserve evidence identifiers and protect confidential information. Record both supporting and contradictory evidence instead of accepting an explanation solely because it sounds plausible.
Apply the Twenty-Question Manufacturer Audit Matrix
The proposed weights below total 100. Adjust them before the audit if project risk requires a different emphasis, then document the approved allocation. Complete a finding record for every applicable question, including risk, actual sample count, finding, score and closure responsibility.
| ID and weight | Audit question | Evidence and pass basis |
|---|---|---|
| A01, 6 | Are drawing and change authorities controlled? | Revisions, approvals and effective lots agree; unauthorized substitutions prevented |
| A02, 6 | Do risk and control documents match the route? | Flow, risk review, control plan and records carry critical requirements |
| A03, 6 | Can finished lots be traced in both directions? | Material-to-shipment drill and reverse trace completed within agreed scope |
| A04, 5 | Are purchased components and sources approved? | Exact identities, incoming checks and source-change approvals |
| A05, 5 | Are wire cutting and stripping controlled? | Programs, first-piece results, strand/insulation checks and restart rules |
| A06, 5 | Is the crimp combination and tooling approved? | Wire-terminal-tool identity, setup, maintenance and verification |
| A07, 5 | Are splice and solder processes qualified where used? | Approved combinations, methods, inspections and hidden-feature evidence |
| A08, 5 | Are routing fixtures and dimensions controlled? | Formboard revision, datums, branch measurement and installation checks |
| A09, 5 | Are terminal seating, seals and locks verified? | Cavity identity, retention method, seal position and secondary-lock checks |
| A10, 5 | Are coverings and strain relief controlled? | Material identity, locations, bend/support requirements and access gates |
| A11, 5 | Are outsourced molding or plating processes controlled? | Subsupplier scope, lot evidence, agreed parameters and change notifications |
| A12, 5 | Are electronic subassemblies controlled where present? | ESD, polarity, component values, programming and software revisions |
| A13, 5 | Is end-of-line electrical coverage verified? | Approved pinout, program/fixture revisions, challenges and unit records |
| A14, 5 | Are qualification and destructive tests traceable? | Allocation, conditions, equipment, raw data and acceptance sources |
| A15, 4 | Is rework authorized and reverified? | Method, disposition, original failure and post-rework results |
| A16, 4 | Do labels and packaging prevent damage and mixing? | Pack validation, revision identity, contact protection and mix prevention |
| A17, 4 | Are capacity and emergency plans realistic? | Bottleneck assumptions, maintenance, recovery and approved alternatives |
| A18, 5 | Are measurement systems suitable? | Calibration status, MSA/GR&R and applicable capability/SPC evidence |
| A19, 5 | Are personnel trained and authorized? | Role matrix, proficiency and change-related instruction updates |
| A20, 5 | Does supplier performance support effective correction? | PPM basis, delivery, returns, repeat complaints and 8D closure effectiveness |
Examine crimp and assembly risks directly
For A06, select the actual terminal-wire combination, compare tooling identity with its approval, and observe first-piece verification. Inspect how a tool change or wire-lot change triggers review. Pull results, height records and section evidence answer different questions; a passing pull specimen does not establish every crimp requirement.
For A08 through A10, compare a finished harness with the formboard and installation definition. Look for tension transferred to terminals, wrong branch datums, partly engaged locks or coverings that conceal uninspected features. The prototype-to-production guide helps distinguish development samples from production-intent approval evidence.
Challenge the test and reaction controls
For A13, inspect an independently approved circuit map and the tester’s current program. Review controlled open, short or miswire challenges appropriate to the coverage. Determine how damaged fixture contacts are identified and how invalid tests are distinguished from valid product failures.
The continuity-testing guide explains these boundaries. Observe the failure reaction without damaging saleable product. Ask whether a valid failed unit remains traceable after repair and whether related units are contained when a shared setup issue is confirmed.
Score Evidence Without Hiding Nonconformities
Use defined zero-to-five anchors
| Score | Evidence anchor |
|---|---|
| 0 | Applicable control absent, contradicted or demonstrably ineffective |
| 1 | Informal practice only; essential requirements unsupported |
| 2 | Partial documented control; important implementation gaps |
| 3 | Implemented control with identified weaknesses needing correction |
| 4 | Sampled evidence meets agreed requirements without significant gaps |
| 5 | Conformity supported by sustained monitoring and verified effectiveness |
Classify the finding separately from its score. Conforming means the sampled evidence meets the stated criterion. Minor means a limited lapse without evidence of systemic loss of control. Major means a systemic breakdown or a failure that threatens required product conformity. Critical means an immediate severe safety, integrity or authorization risk under the agreed criteria. Observation identifies an improvement opportunity without claiming a requirement was violated.
Use N/A only with an approved applicability reason, such as absence of electronic assemblies within the audited scope. Remove its weight from the applicable denominator. Lack of evidence is not N/A. Not Evaluated means the question was not adequately examined; do not assign a score or issue an unrestricted final approval while applicable questions remain unassessed.
Normalized audit score = sum of [(item score ÷ 5) × applicable weight] ÷ sum of applicable weights × 100.
Calculate a final score only after all applicable questions within the approved scope have been evaluated. If scope is restricted, revise and approve the scope explicitly before calculation; do not quietly exclude difficult or unanswered questions. Retain the excluded scope and reasons in the report.
Agree on thresholds and automatic rejection
For an illustrative buyer rule, a score of at least 90 may support approval only when all applicable requirements are assessed, no Major or Critical remains open and mandatory evidence is accepted. Scores from 80 to below 90 may support time-limited conditional approval if risk and contractual obligations permit it. Below 80 does not support approval under this example. These thresholds are proposed decision rules, not ISO requirements.
Treat falsified records, unauthorized critical changes, deliberate concealment, lost required traceability or an uncontrolled safety-critical process as proposed knockout conditions. Define their scope with the customer before auditing. A high weighted score cannot override them, and an auditor cannot grant a concession outside the authorized decision process.
Record Findings and Verify Corrective-Action Closure
Complete the following vertical record for each matrix ID. This avoids a wide spreadsheet on a small screen while retaining the fields needed for an executable audit. An actual audit worksheet may repeat the record twenty times or store the same fields in one controlled database.
| Record field | Entry to complete |
|---|---|
| ID and audit question | Matrix ID, weight and applicable requirement |
| Risk | Failure mechanism and affected product/process scope |
| Evidence to sample | Documents, lots, equipment and observations selected |
| Sample-size requirement | Planned basis, population and actual quantity examined |
| Finding | Objective evidence identifiers and requirement comparison |
| Score | Zero-to-five result with justification, or approved N/A |
| NC level | Conforming, Minor, Major, Critical, Observation or Not Evaluated |
| Owner | Authorized person accountable for containment and correction |
| Due date | Containment, correction and effectiveness-review dates |
| Closure evidence | Cause, changed controls, verification and reviewer |
| Approval consequence | Restrictions, expiry and authorized disposition |
For each nonconformity, separate immediate containment from root-cause correction. Verify changed instructions and actual execution rather than closing the finding from a promised action. Review recurrence across earlier complaints, returns and audits. A20 should include observation windows and consistent denominators for performance data so unlike populations are not compared as equivalent.
Check calibration traceability and measurement suitability where acceptance depends on narrow limits. Use SPC and capability evidence when appropriate to the process and requirements; indices are not meaningful without a suitable measurement system and justified data conditions. Review training authorization, subsupplier notifications and restart controls alongside the corrective action.
Make a Scoped Approval Decision and Work With TONFUL
A supplier scoring 94 with an unresolved Major does not qualify for unrestricted approval under the example rule. A supplier scoring 88 may receive conditional approval only if the authorized buyer accepts the defined deviation and no knockout condition exists. Specify product, site, operations, quantity or period, expiry and required closure evidence.
Audit approval does not release an unqualified harness design. Keep sample acceptance, installation validation and production approval distinct. The IPC workmanship buyer guide supports agreement on revision, class and acceptance authority, but cannot replace project-specific validation.
Share your drawings, product risks, required approval documents and audit scope through TONFUL’s project enquiry channel. Request evidence for the actual proposed site and production route, and agree on open actions before authorizing samples or orders. Verify any certification, equipment or capacity claim against its documented scope rather than assuming it from this checklist.