A custom wire harness drawing tells a manufacturer what to build, how each wire connects, and which details must be checked before production. For a useful quotation, the drawing should identify the wire and connector specifications, pinout, key dimensions, end treatments, assembly features, quantity, and applicable acceptance requirements.
Not every OEM buyer starts with a released drawing or a complete bill of materials (BOM). A reference sample, a connector photo, an early drawing, or a wire list can be enough to begin a manufacturing review. The important step is to separate confirmed requirements from details that still need customer approval.
At Shengxin, we build wire harnesses to customer drawings and reference samples. This guide explains the information we use to review an assembly, prepare samples, and establish an approved manufacturing definition before repeat production.
Quick Reference: Drawing Requirements by Assembly Type
| Assembly type | Most important information | Detail frequently missing from an RFQ |
|---|---|---|
| Cut, stripped or tinned wire leads | Wire style, gauge, color, overall length and end treatment | Exact strip or tin length at each end |
| Crimped terminal wire leads | Wire specification and terminal series/part number | Terminal-to-wire compatibility and crimp orientation |
| Connector wire assemblies | Housing, terminal, cavity positions and pinout | View direction used for cavity numbering |
| Fuse holders and assemblies with electrical components | Component identification, connection method and electrical specification | Component rating versus assembly-level requirements |
| Multi-branch wire harnesses | From-to list (wire schedule), branches, breakouts, lengths and protection | Measurement datums, branch tolerances and connector orientation |
The table below summarizes what to prepare and what is most often missing. The sections that follow explain the technical details for each assembly type. For a complete submission list, jump to the RFQ checklist.
1. What Every Custom Wire Harness Drawing Should Define
Five groups of information form the starting point for a build-to-drawing wire harness project.
Document identification and revision
Give the assembly a drawing number, description and current revision. Identify related documents, such as a BOM, pinout table, schematic, inspection specification or approved sample record. A quotation based on Revision A may no longer apply after connectors, dimensions or materials change in Revision B.
Electrical connections and pinout
List where each conductor starts and ends. For connectorized assemblies, identify the connector reference, cavity number, wire ID, destination and any unused cavities. A schematic shows electrical intent; an assembly drawing also defines physical positions and construction.
Specify the view direction for each pinout: mating-face view, wire-entry view or another clearly labeled orientation. Two drawings can show identical numbering while referring to opposite physical views.
Wire and component specifications
Identify the wire style or applicable material specification, conductor gauge (AWG or mm²), color, conductor construction when relevant, and the required insulation characteristics. Provide the housing and terminal manufacturer, series and part numbers when already specified. Include seals, sleeves, labels and other components that affect the finished assembly.
A housing that looks compatible is not proof that its terminals, locking features or mating header are interchangeable. Any proposed alternative should be reviewed against the actual interface and approved by the customer before use.
Dimensions and physical construction
State the overall length and the points between which it is measured. For branched assemblies, define breakout locations, leg lengths, branch direction and critical tolerances. A wire harness assembly drawing should make these physical details clear even when a separate schematic already defines the circuits. Add connector orientation, wire exit direction, mounting features, clips, labels, heat-shrink positions, sleeving and strain relief where required.
Inspection and acceptance requirements
Specify applicable continuity and pinout checks, required dimensional or visual criteria, and any project-specific mechanical, electrical or environmental tests. If the drawing references an industry workmanship standard, state the applicable document and acceptance class. Test limits and sampling arrangements should be defined in the approved project requirements, not inferred from the standard's name alone.
2. Drawing Details for Different Types of Wire Assemblies
Cut, stripped and tinned wire leads
For simple prepared leads, the drawing may only need a small dimensional sketch plus a wire specification. Show the full length, wire color and style, strip length at End A and End B, and whether either end requires solder-dipped strands, a ferrule or another treatment.
“Tin the end” is incomplete. Indicate which end is treated, the required treated length and any applicable restrictions on solder travel or strand form. A stripped lead and a solder-dipped lead are different manufactured ends; tinning is not a universal step before terminal crimping.
Crimped terminal wire leads
Name the terminal series or exact part number, conductor gauge (AWG or mm²), stripping requirements and any insulation support requirements. If terminal orientation matters in the finished assembly, show it in a detail view. Confirm that the chosen terminal accepts the specified conductor size and insulation outside diameter.
A terminal may physically fit the wire while still being unsuitable for the conductor or insulation combination. Visual fit alone is not a substitute for the relevant manufacturer specifications and approved crimp requirements.
Connector housing assemblies
Specify the connector housing, matching crimp terminals, cavity assignments, cable exit direction and any secondary locks or accessories. For assemblies that mate with a PCB header or another connector, identify the mating interface or provide its verified part number.
A useful pinout table is:
| Wire ID | From | To | Wire | Notes |
|---|---|---|---|---|
| W1 | J1 cavity 1 | J2 cavity 3 | 22 AWG, red | Example only |
| W2 | J1 cavity 2 | J2 cavity 1 | 22 AWG, black | Example only |
Illustrative format only; this is not an actual Shengxin customer pinout.
In the manufacturing drawing, pair the pinout table with a labeled connector view. The view orientation should be unmistakable.
Fuse holders and assemblies with electrical components
For fuse-holder leads, provide the holder part number or approved specification, fuse type where relevant, wire termination method, mounting details and required electrical conditions. A fuse's or holder's individual rating does not automatically establish the rating of the complete wire harness.
For thermistors, indicator lamps, switches or similar incorporated components, identify the exact component or controlled specification, connection arrangement and any relevant parameters. An NTC thermistor description, for example, may require nominal resistance, characteristic/B value, tolerance and sensing arrangement. A generic “NTC wire” label is not enough for component selection or reliable substitution.
Multi-branch wire harnesses
Use a main assembly view and a from-to list (also called a wire schedule). Mark every breakout, reference point and dimension that matters to installation. State which dimensions are critical, where flexibility is allowed, and how any sleeving, taping, protection or labeling is applied. A BOM should link each connector and terminal to the drawing's reference designations.
Where several wire styles or connector families appear in the same assembly, use clear callouts instead of relying on color alone. The drawing must also show any protective treatment that needs inspection before it becomes covered.
3. Five Drawing Gaps That Slow Down a Wire Harness RFQ
These are practical issues to resolve before the drawing becomes the approved manufacturing reference.
- Unidentified connector series. “Three-pin white connector” does not identify a unique housing or terminal. Provide a part number, mating reference or photographs with measurable dimensions.
- Ambiguous cavity view. A numbering diagram without a labeled mating-face or wire-entry view can reverse the intended pinout.
- Undefined end treatment. “Stripped” and “tinned” require separate dimensions and finish requirements. Both ends may be different.
- Length with no datum or tolerance. For a branch harness, define where the measurement starts and ends, including whether connector bodies are included.
- Uncontrolled component substitutions. An alternate terminal, housing or wire may change crimp compatibility or fit. Define which alternatives require customer approval.
Mark unresolved items TBC (to be confirmed) on the working drawing or review list. Do not allow a visually similar component to become an approved substitute by assumption. Use the RFQ checklist below to verify that the open items are captured before sending the inquiry.
4. What If You Do Not Have a Complete BOM or Drawing?
Start with the information you already have. For an initial manufacturing review, a reference sample, photos of both connector faces, a hand sketch, a from-to list or a partial BOM can help identify the assembly and the missing decisions.
Send photographs that show the complete harness and close-ups of each termination. Include a ruler or other measurement reference when dimensions are not available. Indicate which parts must match exactly and where proposed alternatives may be considered.
A preliminary review can establish open questions and possible sourcing options. Production should not proceed from unapproved assumptions. Dimensions, materials, pinout and acceptance requirements must be agreed before the approved build is released.
If you have a physical sample, contact Shengxin before sending it so the sample review and any permitted disassembly can be arranged. See our project preparation guide for the information to include with your first inquiry.
5. Manufacturing Documentation and Sample Approval
A practical custom harness project moves from customer requirements to a controlled manufacturing reference. If an existing assembly is provided as a sample, the workflow may include:
- Review the sample and available requirements. Identify endpoints, connector interfaces, wire characteristics, approximate dimensions and the customer's intended application.
- Prepare a draft manufacturing definition. Record the proposed wire, terminals, housings, pinout, dimensions, protection and unresolved items. The draft documents the intended build; it does not replace the customer's product design authority.
- Confirm critical parts and open questions. Where an exact component is unavailable or incompatible, propose an alternative for customer review rather than making an unapproved substitution.
- Build and submit a reference sample. Check the sample against the proposed definition and submit it with the applicable drawing or specification for customer evaluation.
- Obtain customer approval before repeat production. Record approved revisions, deviations and acceptance requirements. Subsequent production follows the agreed reference.
A Specification for Approval document can identify the customer and supplier part references, assembly description, drawing revision, sample submission date and approval fields. The exact form varies by project. A supplier-prepared form or unsigned customer approval field is not evidence that the customer has approved the assembly.
For an overview of the downstream build sequence, see Wire Harness Manufacturing Process.
6. RFQ Checklist: Ten Items to Send
Use the checklist below when requesting a quote for a custom wire harness or terminal wire assembly.
- [ ] Current assembly drawing, sketch or sample reference, with revision if available
- [ ] Application and installation environment
- [ ] Wire styles, gauges, colors and any specified material requirements
- [ ] Connector housings, terminal series/part numbers and mating information
- [ ] From-to list (wire schedule), pinout and labeled connector-view direction
- [ ] Overall and branch dimensions, measurement references and tolerances
- [ ] End treatments, splices, protection, labeling and special assembly details
- [ ] Applicable inspection, testing, documentation and workmanship requirements
- [ ] Prototype or order quantity and expected repeat demand
- [ ] Requested delivery date, destination and list of unresolved items
You may submit a preliminary package with some items marked TBC. A more precise quote may depend on completing component and manufacturing review. Specified connector availability can affect the procurement window; actual lead time is confirmed for each part number and order.
7. Frequently Asked Questions
Can I request a wire harness quote without a complete BOM?
Yes. Send the drawing, reference sample, photographs or wire list you have, along with expected quantity and any fixed component requirements. Missing details can be identified during manufacturing review. A final build definition still requires approval before production.
Can Shengxin work from a physical wire harness sample?
Yes. We can discuss reviewing a reference sample, recording measurable assembly details and preparing manufacturing documentation for customer review. Contact us before shipping a sample, particularly if disassembly permission, confidentiality or return arrangements need to be agreed.
How should I specify connector pin numbering?
Provide a cavity diagram labeled with its view direction, such as mating-face view or wire-entry view, and pair it with a from-to connection list. Connector shape alone cannot confirm the correct pinout.
Do proposed substitute connectors or terminals need approval?
Yes. Proposed alternatives should be reviewed for their actual electrical and mechanical interface, wire compatibility and project constraints, then approved by the customer before use.
What is needed before mass production?
Confirm the drawing revision, material and terminal selection, pinout, sample evaluation outcome, acceptance requirements and any approved deviations. The released manufacturing package should reflect the customer's final approval.
Send Your Drawing or Sample for Review
Attach your latest drawing or share the details available today. Partial information is acceptable for an initial review. Include the intended quantity and application, and flag any open decisions. We can review the assembly definition and identify what is needed for a manufacturable, quote-ready specification.
