The Aerospace Wiring Harness Questions Every Procurement Manager Should Be Asking

Aerospace wiring harnesses operate in environments that push components to their limits. Temperature extremes, vibration, electromagnetic interference, and the absolute requirement for consistent, long-term electrical integrity all place demands on the harness that general-purpose manufacturing processes are not designed to meet.

Weight is a constraint that does not exist in most other sectors. Every gram matters on an aircraft, and a wiring harness designed for an automotive application is unlikely to be optimised for weight without specific engineering input. The materials, wire gauges, connector types, and routing geometry all influence the finished weight, and all need to be considered from the outset.

And the documentation burden is substantial. Traceability of components, test records, engineering change control, first article inspection reports, and compliance evidence are not optional extras in aerospace supply. They are part of the product. A manufacturer that cannot provide them is not a viable partner regardless of how competitive their pricing appears.

1. What certifications do you hold, and are they current?

This is the starting point, but it should not be where the conversation ends. ISO 9001 is the baseline for quality management in manufacturing. It demonstrates that documented processes exist and are subject to external audit. It does not, on its own, confirm that a manufacturer is equipped for aerospace-specific requirements.

Ask to see the current certificate, not just a logo on the website. Check the scope statement on the certificate, which defines exactly what activities and product types are covered. A certificate that excludes cable assembly or wiring harness manufacture from its scope is not evidence of approved aerospace capability, whatever the headline standard says.

UL approval for wiring harness supply is a further credentialing step that confirms compliance with recognised safety and electrical standards. It is worth asking whether the manufacturer holds this and, again, what the approved scope covers.

What good looks like: Current ISO 9001 certification with a scope that explicitly covers cable assembly and wiring harness manufacture. UL approval for wiring harnesses. Willingness to provide certificate documentation without being prompted.

2. Can you demonstrate actual aerospace manufacturing experience?

Any manufacturer can claim to serve the aerospace sector. The relevant follow-up is whether they can evidence it. Actual experience means having manufactured assemblies used in aerospace programmes, not simply having an AS9100-aligned quality system or a statement of capability on a website.

Avionics control systems, communications wiring, power distribution harnesses, and defence-grade cable assemblies each have different requirements, and a manufacturer with genuine depth of experience will be able to speak to specific challenges and solutions rather than in general terms.

3. How do you manage component traceability?

Traceability in aerospace supply means being able to identify, for any assembly delivered, exactly which components were used, where those components came from, and when they were manufactured. If a batch issue is identified after delivery, traceability allows a manufacturer to tell you precisely which assemblies are affected, and which are not.

A manufacturer without a robust traceability system cannot give you that answer. The implications of that in an aerospace context, where a grounding or inspection requirement could affect an entire fleet, are significant.

Ask how components are documented at goods-in, how that information is linked to individual work orders, and how finished assembly records are retained. The answer should be specific and procedural, not general.

What good looks like: A documented traceability process from component receipt to finished assembly. Defined retention periods for records. Ability to produce assembly history for any batch on request.

4. What does your testing process look like?

There is a significant difference between a manufacturer that tests samples from a batch and one that tests every assembly before it leaves the facility. In aerospace supply, the latter is the expected standard.

SIC 100% tests every product line prior to shipment. That means every assembly, not a statistical sample. The test records for those assemblies are part of the delivery documentation and are available upon request.

Ask what test types are applied, what the pass criteria are, and how failures are recorded and managed. A credible answer will include continuity testing as standard, with additional testing for shielding performance, insulation resistance, or other parameters depending on the specification.

• Continuity testing: verifies all connections are complete and correctly made
• Insulation resistance testing: confirms wire insulation integrity under voltage
• High-pot (hi-pot) testing: applies elevated voltage to identify insulation breakdown
• Shield continuity: confirms correct grounding and shielding where specified

What good looks like: 100% end-of-line testing on every assembly. Test results retained as part of the batch record. Clear failure management process.

5. What is your processing capability for aerospace wire specifications?

Aerospace wiring harnesses frequently involve wire gauges and connector types that are outside the range of general-purpose manufacturing equipment. If a manufacturer cannot process the specific wire gauge or terminate the specific connector type your assembly requires, that is a fundamental constraint regardless of any other credentials.

SIC processes cable from 30 AWG to 3/0 AWG (95mm²), covering the full range from fine-gauge signal wire to heavier power conductors. Our Komax Alpha 530, one of the only machines of its kind in the UK, delivers precision automated crimping across a wide range of termination types, with fast setup times and highly consistent output. This level of processing capability is not universal among cable assembly manufacturers.

Ask specifically about the wire gauge range the manufacturer can handle, the connector and termination types they can process, and whether they have the equipment to validate crimp quality to the required standard. In aerospace, crimp pull-force testing and cross-sectional inspection are common validation requirements.

What good looks like: Clear statement of wire gauge range, connector capability, and crimp validation processes. Specific equipment references where relevant.

6. How do you handle prototypes and pre-production validation?

The point at which problems are cheapest to resolve is during prototype and pre-production. A manufacturer that moves directly from a drawing to volume production without a formal validation stage introduces risk that should not be accepted in an aerospace programme.

Ask what the prototype and pre-production process looks like, what documentation is produced at the first article stage, and how the results of that stage feed into the production process before volume runs begin.

What good looks like: A defined prototype and pre-production stage. First article inspection report produced and shared. Formal sign-off before volume production commences.

How do you manage engineering changes during an active programme?

Design changes are a reality in aerospace development programmes. What matters is how a manufacturer handles them. Verbal agreements or informal email chains are not adequate for a regulated supply chain. Ask for a description of the engineering change order process, including how changes are documented, who approves them, and how version control is maintained across assembly batches.

A manufacturer without a defined engineering change process is a programme management risk, not just a quality risk. The same drawing should not produce two different assemblies depending on when the order was placed.

How do you source and verify your components?

Counterfeit components are a documented problem in the aerospace supply chain. Counterfeit connectors, wire, and passive components have entered supply chains through third-party distributors and grey market sources. The consequences of a counterfeit component in an aerospace assembly can be severe.

Ask where the manufacturer sources its components for aerospace work, whether they use authorised distributors, and what their incoming inspection process looks like for electrical components. A manufacturer that sources components solely on price from unverified suppliers should not supply to an aerospace programme.

What good looks like: Named authorised distribution relationships. Documented incoming inspection for components. Ability to provide material certificates for safety-critical wire and connector types on request.

What are your realistic lead times, and how do you handle urgent requirements?

Lead time transparency matters more in aerospace than in most sectors, because programme delays in aerospace are exceptionally costly. A manufacturer that gives optimistic lead times during the sales process and then fails to deliver is more damaging than one that quotes a longer lead time accurately from the outset.

Ask for lead times broken down by stage: procurement, production, and test. Ask what happens if a component is on allocation or unavailable. And ask how urgent requirements are handled, whether through held stock, expedited procurement routes, or scheduled flexibility.

Can you scale with the programme across its lifecycle?

Aerospace programmes frequently begin with low-volume prototyping and development assemblies and scale to higher volumes as the programme matures. A manufacturer that can handle the prototype stage but not production volume, or vice versa, creates a transition problem that must be solved mid-programme.

SIC manufactures across the full range from low-volume, high-complexity development assemblies to high-volume production runs, and can accommodate both within the same production facility. That consistency across the programme lifecycle removes the supplier transition risk that is common when development and production suppliers are different organisations.

Does SIC hold AS9100 certification?

SIC currently holds ISO 9001 and ISO 14001 certifications, along with UL approval for wiring-harness supply and Made in Britain certification. If your programme has a specific AS9100 requirement, we recommend discussing the full documentation and compliance requirements directly with our team. Our quality management processes are aligned with the rigorous standards expected in the aerospace supply chain, and we can provide full documentation upon request.

What is the minimum order quantity for aerospace wiring harnesses?

SIC maintains an extensive component inventory that allows us to offer accommodating minimum order quantities, including for low-volume prototype and development runs. We do not impose minimum order quantities that are impractical for the development stage of an aerospace programme. Contact our team to discuss your specific requirements.

How does SIC handle first article inspection?

Every new product line goes through a prototype and pre-production stage before volume production begins. This includes first article build, inspection against the drawing and specification, and a formal sign-off process before volume runs commence. Documentation from the pre-production stage is available as part of the product record.

Can SIC process fine-gauge wire for avionics applications?

Yes. SIC processes cable from 30AWG to 3/0AWG (95mm²), covering the full range from fine-gauge signal and data wire used in avionics and instrumentation to heavier power conductors. Our Komax Alpha 530 automated wire processing equipment delivers consistent, validated crimp quality across this range.

The questions in this article are not designed to make the procurement process longer or more complicated. They are designed to give the process the rigour that aerospace supply demands. A manufacturer that can answer each of them clearly, specifically, and with supporting evidence is one that understands what the sector requires.

A manufacturer that struggles to answer them, or that deflects with general statements about quality commitment without substantiating them, is one that carries programme risk regardless of how competitive their pricing appears.

SIC Ltd has been manufacturing wiring harnesses and cable assemblies since 1964. If you are assessing suppliers for an aerospace wiring harness requirement and would like to discuss our capability in detail, contact our team today.

Call 01792 957009, email enquiries@sicltd.com, or use the contact form at sicltd.com.