Checking the condition and replacing the battery wires (BMW 5 Series E28)

Examination

Periodically inspect the entire length of each battery cable for damage, cracks, burnt insulation, and corrosion. Poorly maintained cable ends can cause difficulty starting and poor engine performance.

If your car radio has an anti-theft system, make sure you know the correct activation code before disconnecting the battery. Refer to Section 1 for information before disconnecting the wire Anti-theft audio system and instrument cluster language.

If a message in another language appears on the instrument panel display after connecting the battery, refer to Section 1 for the language setting procedure Anti-theft audio system and instrument cluster language.

Check the ends of the wires where the wires connect to the battery terminals for cracks, loose wires, and corrosion. The presence of a white, loose substance under the insulation of the wire tip is a sign of corrosion and the wire should be either cleaned or replaced. Check the terminals for bending, proper mounting bolts, and corrosion.

Replacement

When disconnecting wires, always disconnect the negative cable first and reconnect it last. This reduces the risk of accidentally shorting. Even if you are replacing only the positive cable, be sure to disconnect the negative cable from the battery first (for more information on removing battery cables, see Chapter Routine car maintenance).

1. Disconnect the old wires from the battery, then move them to different sides and disconnect them from the starter solenoid relay and housing. Remember the routing of each wire so that you can install it correctly later.



2. If the old wires need replacing, take them with you to the store. It is vital to replace the wires with identical ones. The wires have features that make them easy to distinguish: the positive wire is usually red, has a larger cross-section, and has a larger diameter tip; the negative wire is usually black, smaller in cross-section, and has a slightly smaller diameter terminal tip.

3. Clean the threads of the traction relay terminals and the housing from rust and corrosion with a wire brush.

To prevent future corrosion, apply a thin layer of battery corrosion inhibitor or petroleum jelly to the terminal threads.

4. Connect the wires to the terminals of the traction relay and the housing and tighten the nut/bolt firmly.

5. Before connecting a new wire to the battery, make sure that the wire reaches the terminal without tension.

6. Connect the positive wire first, then the negative wire.

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