Q: Do wiring harnesses need to be replaced?

As automotive electrical systems increase with each model year, so does the amount of wiring required to operate them. BMW says their current models can contain up to a mile of wires weighing as much as 130lbs! All of this wiring acts as the vehicle’s nervous system. Electrical current is carried to perform tasks and electrical signals transmit information to and from computers. Most of the wires are bundled together into groups called harnesses. Harnesses are wrapped in a protective covering and then routed and secured throughout the vehicle to protect them from damage.

But life for vehicles can get tough. Constant vibration, flexing, exposure to heat and cold, water, ice, and salt can all eventually take a toll on the wiring. Wiring harness damage is also not unusual when a vehicle has been involved in a collision.

Many vehicles will go through their entire service life without any issues related to the wiring harness or its connections. But it is not unusual when diagnosing a problem with a vehicle system to eventually locate the root cause at a damaged wire, terminal, or connector. Since wiring harnesses are frequently installed in hard-to-reach locations, finding the exact problem area of the “short” circuit or “open” circuit can frequently be a challenge for a technician.

Once the wire problem is located, typically the damaged wire or two can be repaired, or a new piece of wire can be spliced in. But sometimes the damage is more extensive, wires are melted, or a hard-to-reach location makes repair impossible. In these types of situations an entire portion of harness may need to be replaced. Since harnesses come in all sizes from small and simple, to large and complex, the cost to purchase and install them covers a very broad range. Some vehicle manufacturers also specify harness replacement, rather than wire repair, on certain sensitive safety systems such as airbags. This type of specific guidance varies between manufacturers and can be found in their service information.