BTW my voltmeter does indeed have a diode setting - how do I test? What is a good reading?
A diode is a one-way valve for electricity. The diode setting on your meter will read the forward biased voltage drop when the diode is conducting, usually around .500, and when reverse biased, by reversing the meter leads, will read the same as when the meter leads aren't touching anything.(one of my meters reads 1., and another one reads 3..) There are 6 diodes in the rectifier, and they need to be tested in both directions.
With the meter black lead connected to the rect red wire, probe each of the yellow wires with the meter red lead. Each should read about .500. Next reverse the meter leads, and check each yellow wire again: now they should each read whatever your meter shows with the leads not touching anything.
Now, place the red meter lead on the rect green wire, and probe each yellow wire with the meter black lead. Again, the results should be about .500, and after reversing the meter leads each yellow should read the same as open meter leads.