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Find Bad Battery Cable



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There are times when it is intuitively obvious that replacing a vehicle’s battery cable is critical. Other times, the need to replace a battery cable is not clear to the naked eye. When a vehicle does not start, or the alternator light comes on, there are several ways to determine what really needs to be replaced.

Some of the visible signs that a battery cable needs to be replaced include some common-sense indications that it will no longer function safely or effectively. These visual signs include:

Breaks in the protective coating of the wire, particularly away from the connectors.
Corrosion that resists all normal means of removal, such as wire brush removal or cleaning with baking soda paste.
Clear fraying or breaks in strands of copper.

However, there may be other reasons that the battery cable needs replaced that cannot be found on a visual inspection. Many cars after 1980 have a specially designed cable between the battery and the starter or between the battery and the alternator called a fusible link. The cable itself acts as a fuse to keep a malfunctioning alternator from overcharging the batter or keeping a failing starter from over-drawing from the battery.

A simple check with the continuity test of a multi-meter can let you know if each cable “leg” is functioning properly. Someone familiar with the use of a multi-meter should only do this with the engine off. The tips to checking the continuity of the various cables includes:

Disconnect your positive terminal (“hot”) from your charging system.
Using the resistance/continuity check on the multi-meter, verify that there is close to 0 resistance on each “leg” of your charging system. A leg includes: the ground wire, the positive wire from the battery to the starter, and the wire from the alternator to the battery.
Any wire with high resistance is suspect.

Both a vehicle repair manual such as Haynes, or various sources on the internet can help you identify highly suspect wires that may contain a fusible link on your particular vehicle. However, remember if the battery cable needs replaced for physical damage, it is critical to ensure that the new cable is routed to be safe from similar damage. If the cable needs replaced due to a tripped fusible link, it is critical for the do-it-yourselfer or a mechanic to determine what caused the over-amperage. If not addressed, there is a chance the problem will resurface.

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