Many car owners have had problems starting their car with what appears to be a dead or weak battery, only to have the battery tested and told that it is in good condition. Sometimes this symptom is caused not by the battery, but by corroded or damaged battery cables that provide such high resistance to the electrical circuit that it does not provide sufficient current to power the starter and fire up the engine. With the help of a friend, you can test your battery cables and determine whether they are bad or not.
Step 1 Attach the positive (red) lead from the multimeter to the positive battery terminal.
Step 2 Set the multimeter to measure voltage. Have the person helping you start the engine now while you keep a close eye on the multimeter. The voltage reading should be very close to 0. If the reading is 0.3 volts or more for a small four-cylinder engine, or 0.5 volts or more for larger six- to eight-cylinder engines, the cables are bad and should be replaced.
Test the negative battery cable in the same way. Attach the negative (black) lead from the multimeter to the negative battery terminal. The voltage reading should be very close to 0. A reading of 0.3 volts or more on this negative side is reason to replace the cable.
Things You'll Need: Digital multimeter
Warnings: Do not try to use a voltmeter set to ohms, or an ohmmeter to measure the resistance of the battery cables in your vehicle. Most ohmmeters that are commonly used in automotive work do not have the required sensitivity to measure the very small, but very significant resistance in the cables.
