Electrical Harness Maintenance

Electrical Harness Maintenance By Dan Warchol September 2000 Author's note: Unison Industries and specifically the author of this article would like to acknowledge the contributions of Pratt & Whitney to the completion of this article...


Thermocouple Lugs
If the harness contains thermocouple circuitry, inspect the thermocouple lugs for any damage. Also check the wires for damaged insulation. Confirm that ground pigtails and ground lugs are acceptable. If necessary, replace the harness assembly.

Wire Cable Condition
ImageExamine the harness for evidence of heat distress that could cause the harness to be discolored. Heat could also cause the harness insulation to melt, bubble and crack. If heat distress is noted, locate the heat source and take appropriate actions to correct the problem. It may be necessary to adjust the harness routing (by eliminating excess slack), to move portions of the harness that are too near hot tubes or components.
Check for any evidence of chafing of the wire bundle. If metal braid is exposed, take the appropriate actions to alleviate the problem. Chafing may result from a worn or loose mounting clamp, or rubbing against a bracket, tube, fastener or some type of external component.

Lacing Ties
Check lacing ties for tightness. Ties should be tight and not able to be move along the wire bundle. Discolored ties are normal and it is not necessary to replace them unless they are loose. If ties are loose, remove and replace in accordance with the CMM.

Cleanliness
ImageHarnesses are typically designed to withstand exposure to various fluids that are expected in the given application. However, they should be kept clean if possible. Wipe excess fluids and other materials from the harness. If a fluid leak has occurred, check for fluid in the connector backshells. Remove the fluid and clean the backshells if necessary. Make sure the connector insert is clean and free of any fluids. Try to eliminate the leak or source of fluids so the harness won't be exposed to the same harmful fluids in the future.

Contacts
Examine connectors to ensure the contacts are in good condition. Check pin contacts for bending, corrosion and other damage. Check socket contacts for corrosion and damage. Replace all contacts that exhibit these undesirable conditions. Using the appropriate tools per the CMM (not probes or paper clips), make sure that contacts are locked in position and have not backed out or pushed into the connector grommet. Replace the connector if any of the contacts can not be locked in position.
If worn contacts or intermittent circuits have been identified, check the contacts for engagement force with a new mating pin or socket. A slight force should be required to insert or remove a mating contact.

ImageIn-Shop Maintenance for Open Bundle Harnesses
Preliminary Examination
Lay each harness out on a bench and examine for any evidence of damage that needs to be corrected. Look for chafing, nicks, thermal distress, damaged connectors, backshells, terminal lugs, etc. Tag the damaged areas for repair.

Cleanliness
Clean the accessible portions of the harness to remove any fluids or other contaminates that have accumulated. Be careful to protect the front face of all connectors. Connector faces and contacts should be cleaned using the procedures defined by the CMM.

Electrical
Perform a complete electrical check of the harness using the CMM procedures. During the electrical testing, move the harness on the inspection table to expose any intermittent short or open circuits. Repair any damage using the CMM procedures.

Connectors
All connectors should be completely disassembled so an adequate inspection can be performed. The coupling ring should be relatively free turning and should have indication that the self-locking mechanism is working. Some plug style connectors have an internal metallic EMI band on the barrel of the body (below the alignment keys). The EMI band should be undamaged. The connector face should be undamaged with no chips if it is a hard-faced connector. For soft-faced connectors, no tears, bubbles, puncture marks or swelling of the connector grommet are permitted. If any of the above damage exists, replace the connector per the CMM procedures.
Check the rear grommet of the electrical connector. If excessive distortion of the wire entry holes is noted, replace the connector per CMM procedure. Unwired positions should have a contact sealing-plug installed.
Even if worn contacts or intermittent circuits have not been identified, it is still a good idea to check the contacts for engagement force with a new mating pin or socket. A slight force should be required to insert or remove a mating contact. Replace the pin or socket if they fail this test per the CMM procedures.

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