Most quotation delays and first-sample rejections on a wiring harness trace back to a drawing that was released with a question still open. This checklist is for the engineer who owns the drawing. It lists what to confirm before the drawing goes to a manufacturer such as APAR, whose automotive and EV harness and railway coach harness services build to the customer drawing.
Electrical
- Every circuit has a wire size chosen from the load current and the permitted voltage drop, checked against the longest run. The voltage drop chart gives worked examples for 12 V and 24 V.
- The protective device for each circuit is named, and the wire is rated above it.
- Screened, twisted-pair and high-voltage circuits are marked, with the screen termination method stated.
- Shared grounds and splice points are shown on the drawing, not left to the manufacturer.
Mechanical
- Length tolerances are stated for the trunk and for every branch.
- Breakout positions are dimensioned along the trunk, and each branch has a defined length.
- Fixing points, clips and grommets are located, and the bend radius at each connector exit is respected.
- The maximum bundle diameter is stated where the harness passes through a panel hole or conduit.
Environment
- The peak and continuous temperature at each section of the route is recorded, and the insulation class is chosen from it.
- Exposure to oil, fuel, coolant, water or cleaning fluids is stated for each zone.
- Sealing is specified at each connector, with the seal and cavity plug part numbers. The connector sealing chart explains the IP ratings.
- Protection is specified for each zone: sleeve, conduit, tape or grommet. See the protection materials chart.
Connectors and terminals
- Each connector has a full part number, a terminal part number and a wire size range that matches the wire on the drawing.
- Keying, locking and any secondary lock are specified.
- The crimp tooling or crimp specification is named where the terminal manufacturer requires it.
Identification and documentation
- Wire, branch and connector labels follow a stated scheme. The labelling and identification guide describes one.
- The bill of materials lists every item, including tape, sleeving, ties and labels.
- The drawing carries a revision number, and the revision is repeated on the bill of materials.
- The required tests are stated, with the acceptance criteria. The harness testing guide lists the standard checks.
Once these items are closed, the drawing can go into the RFQ checklist process with fewer queries.