Guidelines to Successful Harness Print Creation
The question is often asked, “What should be included on a wire harness print?” In answer, it is important to consider its purpose and who will reference it. The harness print is a communication tool, used across many functions of a business, that documents the wiring requirements of some portion of an electrical system. The creation of a wire harness print is an engineering function. The main purpose of the task is to design a wire harness schematic that meets the electrical needs of the final product in its end use environment. However, there are other uses of the print that should be considered. Purchasing, Production, Quality and Service will also reference the print to fulfill their duties. Also, outside of your own company, a supplier will need to use the print to build the harness correctly.
Engineering should consider such requirements as wire type, connector and terminal information, covering/bundling options, length measurements, “From/To” list, diode direction, resistance values and other general notes.
- Wire type options include insulation type or jacketed cable requirements.
- Connectors, terminals, boots, strain reliefs, terminal locks will need specified. Remember to use the Manufacturer’s part numbers so that a supplier can understand exactly what you need.
- The main covering or bundling options include split tube convoluted looming, pre-woven braided sleeving, direct braided looming, jacketed cable and zip ties, but there are many variations of each that need spelled out if it is critical to the end use environment.
- Length measurements, including reference locations and tolerances.
- A list that includes where each wire comes “From” and where it goes “To” is simply referred to as a “From/To” list. Both ends of each wire will go from one point to another, even if it is a splice or a blunt cut. The point to point information displayed in the “From/To” list can provide most of the criteria needed to produce a wire harness. Connector pinouts, spliced wires, circuit names, gauge sizes and twisting/shielding requirements can all be posted in this list.
- Diode direction and resistance values should be noted, if applicable.
- There are other notes that apply to the construction of your harnesses that you may not want to include on every print. Items like filling unused positions, allowing industry approved equivalents to save cost, harness labeling and packaging requirements need to be addressed. Some companies will subscribe to an industry standard like the IPC/WHMA-A-620 Requirements and Acceptance for Cable and Wire Harness Assemblies to cover any bases that were missed. Other companies will establish their own specification document that is referred to in the general notes section of the print.
- If you choose the IPC/WHMA-A-620 as your default for requirements not listed on your print, a class should be chosen. If you do not pick the class, the manufacturer will choose it for you. Class 1 is for general electronic products; Class 2 is for dedicated service electronic products and Class 3 is for high performance electronic products. The medical and aerospace industries often choose Class 3 and must pay a premium for this, as Class 3 adds expensive process control requirements to the manufacturing process.
Purchasing will take the finished document, complete with a part number, description and revision level, and send it out for quoting. If the print is sent to multiple suppliers for quoting, it’s very important that the print is specific enough to get an “apples to apples” quote for comparison studies. If there is room for varying interpretations, a supplier may come in with a low price, but not build to the designer’s intent. Suppliers will often ask for an estimated annual usage (EAU) so that they can quote appropriately. From a top-level view, it is wise for the quote review team to consider lead times and minimum order quantities in addition to the quoted piece price.
Wire Harness Supplier will use the print to determine the cost of building the harness. In a manufacturing setting, the wire harness print (also called a customer print) carries full authority and is referred to often and by many people in the facility. The quoting/launch team will use it to create a Bill of Materials, creating new part numbers as needed. Quotes are sent out further up the supply chain for pricing based on the EAU from the OEM. Once the parts cost is determined, along with the cost of manufacturing, a quote is generated and approved by the supplier’s team to be sent back to the OEM. If a purchase order is sent to the supplier, the wire harness print is further used to develop a wire processing list, splice details, manufacturing instructions, a test program and inspection criteria. Shop floor personnel will use the print to build and inspect the harness to verify quality conformance.
Once the harness is delivered to the OEM, a Quality inspector may use the print to check the actual harness to the print’s specifications. During installation, the print may be used to finalize some electrical connections. At an “end of line” test, the print may be referenced during troubleshooting. Out in the field, Tech Support or a Field Service mechanic may look at the print to help diagnose a problem.
As you can see, a successful print is a document that will be used by many people in multiple functions. A great print will result in the same interpretation by people who will never meet in person to discuss the creator’s actual intent. Maybe you are part of a small growing company today and you wear a lot of different hats. Sometimes growth happens fast and people are added to an organization rapidly. Some people seem to understand the spirit of a print, while others seem to only see the letter of the print. This can create confusion and contention. If a print is created and maintained correctly, there can be peace.
Notice that I add “maintained” to the last sentence. Another common pitfall in the industry today is that there is a lot of tribal knowledge shared between OEM’s and suppliers that is not represented on the current print. Changes are made to the harness design, but not kept current on the print. In today’s job-hopping culture, some of the relationships that worked well in the past cause problems today because the people who knew what to do are not there anymore. Companies find themselves in a tight spot when they struggle to select a new supplier because the documentation that they have doesn’t match what they are currently using.
Maintaining a print means keeping the current print up to date with the desired result and making sure that everyone who uses the print has the latest revision. Revision levels should be listed on the print, as well as a log of everything that changed from the last revision. The new revision should be sent to the supplier to update their systems and provide new pricing, if applicable. Production, Quality and Service should also be notified of the change to the current drawing for that part number. There can only be one current drawing revision for each part number.
Since so many people will reference your print, keep this in mind when you create it:
A successful print will provide:
- Technical information to meet the electrical needs of the OEM system in its end use environment
- A resulting harness that does not vary from the intent, even if produced by multiple suppliers
- A consistent harness when produced by different people each time
- Revision tracking to eliminate confusion through a revision change