Wire Harness Drawing Requirements & Notes

The documents in a complete package

Document	What it defines
Schematic	The electrical design: which circuits connect, and why
Wiring table (from-to list)	Every wire: from connector and pin, to connector and pin, wire type, size, color, length and identifier
Harness layout drawing	The physical harness at full size or to scale: branch positions, lengths, tolerances, connector clocking, labels and protection
Bill of materials	Every part, with manufacturer part numbers and quantities
Notes	Workmanship standard, tests, marking, materials, approvals

For simple point-to-point cable assemblies, these can often fit on one sheet. For complex harnesses, the wiring table is usually a separate sheet or a controlled file.

Layout drawing: the geometry

Lengths measured from defined points. State where each length is measured from, for example from the rear face of the connector or from the center of a breakout.
Tolerances that match installation. A tolerance tighter than the product needs adds cost without improving fit.
Breakout positions and branch lengths, with an identifier for each branch.
Connector clocking. Where orientation matters, show the view direction and the key position relative to a reference.
Protection by zone. Which sleeving, braid, conduit or tape covers which section, and where it starts and stops.
Bundle securing: tie or lacing type and spacing, and any clamps or grommets supplied with the harness.
Label positions, measured from a defined point.

Connector views and pinouts

State whether each connector view is from the mating face or from the wire entry side. A view that is not labeled is the most common reason a harness is built as a mirror image of the intended one. Include unused cavities and whether they need sealing plugs.

Notes that belong on every drawing

Workmanship standard and class, for example "Build and inspect to IPC/WHMA-A-620, Class 3", with the revision, and whether later revisions are acceptable. See choosing a class.
Electrical test requirements, with parameters and sampling. See cable assembly testing.
Marking: what the label says (part number, revision, serial or date code), the label material, print method, text height, durability and location.
Wire identification, if individual wires are to be marked, and how.
Substitution rule: approved alternates listed, or "no substitutions without written approval".
Material requirements: restricted substances (such as RoHS or REACH, if applicable), flammability ratings, and qualified-product requirements.
Crimp and solder process standards, where they differ from the workmanship standard's defaults.
Unspecified dimensions and tolerances: a general tolerance note.
Export control marking, if the drawing is ITAR or EAR controlled.

Wiring table: a minimal layout

Wire ID	From	To	Wire spec	Size	Color	Length
W1	P1-A	J2-3	[wire spec]	[AWG]	[color]	[length]
W2	P1-B	J2-4	[wire spec]	[AWG]	[color]	[length]
SH1	P1 backshell	J2 backshell	Shield termination method per note

Add columns for splice identifiers, twisted pairs, and termination part numbers where they vary by wire. Every connector reference (P1, J2) should match a label on the layout drawing and a line on the bill of materials.

Bill of materials: what to lock down

Connectors, backshells, contacts, seals and sealing plugs, with full manufacturer part numbers.
Terminals and splices, with the wire size range each must accept.
Wire and cable by specification or manufacturer part number, not only by gauge and color.
Protection materials: sleeving, heat shrink, tape, conduit, with size.
Labels and marker materials.
Hardware supplied with the harness: clamps, grommets, cable ties.

"Or equivalent" without a definition invites a supplier to choose. If equivalents are acceptable, say what makes a part equivalent, or list the approved ones.

Common drawing mistakes

Connector view direction not stated.
Wire lengths in the wiring table that do not agree with the layout drawing.
A wire size outside the range of the specified contact.
Shield and drain terminations not defined.
No workmanship class, so each supplier assumes its own.
Test notes with no voltages, limits or sampling.
Revision letter on the drawing not matching the revision on the purchase order.

Ask for a design-for-manufacture review

Before release, ask a prospective supplier to review the drawing. A good review will flag contacts that do not suit the wire size, tolerances that cannot be measured on a finished part, labels that cannot be placed where drawn, and components with availability problems. It costs little and prevents most first article failures.

What to ask a supplier

Which notes on this drawing would you interpret differently from how they are written?
Can you build and measure the part to these tolerances with your formboard method?
Which components would you flag for availability?
Can you work from our CAD harness data, or do you need a flat drawing?

Common questions

Does a cable assembly need a layout drawing?

A simple point-to-point cable assembly may only need a length, connector callouts, a pinout and notes. Once it has branches, labels at set positions or clocking requirements, a layout drawing helps.

Should the wiring table be on the drawing or a separate file?

Either works if it is revision-controlled with the drawing. A separate machine-readable file can also be used to generate test programs, which reduces transcription errors.

How should lengths be toleranced?

Base them on how the harness is installed. Many drawings use a tolerance that grows with length; your own standards, or your customer's, should decide the values.