Step-by-step guide to testing battery and charging circuit

November 27, 2009

1. Place the multimeter across the battery terminals. A fully charged battery should produce a reading of 13.2V. Check the earth strap, all wires and connections are sound.

2. The Euro Plug on the alternator has three slots. The two larger tabs form the B+ terminal that feeds the battery. The smaller D+ terminal supplies ‘excitation’ power to the alternator through the charge warning light circuit.

3.To test if the charge warning circuit is okay, make up a small jumper lead by fitting a male ‘Lucar’ terminal on to one end of a piece of wire. Fit this into the smaller D+ connection and place the other end on to a good earth.

4.With the jumper wire connected, the warning light on the dash should come on - if not it is either a blown bulb or poor connection. The alternator will not work unless it receives current from this circuit via its D+ connection.

5. To establish if voltage is reaching the alternator, place the multimeter’s red (+) probe into one of the B+ terminals in the Euro Plug and the black (-) probe on to a good earth and the screen should show battery voltage.

6.The multimeter is connected in parallel and the ammeter in series in the circuit between the alternator and the Euro Plug. With the engine running the battery should charge at 14 to 15V and the amps should respond to load.