Wiring in a larger alternator

[HO455]

An oscilloscope makes detecting bad alternator diodes really easy but, you can also detecting diode failure with a regular multimeter.

The diode bank in the alternator charges the 3 phase AC voltage the rotor and stator make into DC voltage.

If you have a failing or failed diode you will be getting AC voltage output from the alternator. This can cause several different symptoms like flickering lights and humming from stereo. If you check for voltage with a multimeter but put the scale to AC volts instead of DC if there is a diode problem your meter will show AC voltage. Do the voltage test while changing the RPM of the engine.

Taking your alternator to the local generic parts store for testing may not reveal this problem as the alternator may still be capable of rated output.