How do you test the diodes of your alternator
 

or any diodes for that matter ?

Use a multimeter and set it to the resistance measurement setting.

You should get a reading one way and if you turn the leads around, you won't get any reading. i.e. it only allows current to flow one way.

Cheers Jakes

This won't give accurate information, i.e. does not work always.

In my case all the diodes showed up good when measured with multimeter, so I took the alternator to the shop because I did not find anything wrong with it. Well, when they hooked it up to the test bench and tested it with enough current, the machine showed that 2 of the diodes were faulty.

Cool, I did'nt realise that. But I do remember that on the more expensive multimeters, some of them had specific diode and transistor test ports. Nice to keep in mind though.

Thanks Jakes

The diode is like a check valve for electricity. It will only allow current to flow in one direction. The diode has two terminals the anode and the cathode. The symbol looks like this. http://forums.pelicanparts.com/uploads/diode.jpg Current will flow through the diode when a Positive battery voltage is applied to the Anode and the Negative battery voltage is applied to the Cathode. The diode will block current flow when a Negative battery voltage is applied to the Anode and a Positive battery voltage is applied to the Cathode. The band or stripe line on one side of the diode indicates the Cathode side of the diode.