TESTING A CONVENTIONAL ALTERNATOR

1 Using a multimeter, measure the voltage at both battery terminals when the ignition and all electrical ancillaries are switched off. On newer vehicles, wait for all ECUS to shut down.

2 Start the engine with all electrical ancillaries switched off. The voltage should stabilise at around 13.5-14.5 volts. Higher, or lower, readings could mean that the alternator is faulty, which might have damaged the battery.

3 Switch on as many electrical ancillaries as possible and raise the engine speed to around 1500rpm. The reading should be similar to that recorded with no load and it should not dip below 13 volts.