Using resistance (ohm) meter, bad diodes normally either short (0 ohms) or read open (infinity). Most meters that read resistance have a diode check feature on them. Hooking the meter leads in one direction on the diode it will read a different resistance then when you reverse the lead polarity to the opposite direction on a good diode. Sometimes diodes can read fine with a meter but once the larger voltage and current hit them they open up. Regulators can be even a little more tricky. The diagram I found at Sears must be sort of a generic one. It does not show the diode outside of the regulator.
What you can do is try to verify the AC output of the alternator, then verify with your voltmeter the DC output of the diode to the regulator. If you have power into the regulator then it is probably a bad regulator. On the input side of the regulator (output of the diode) you should see a change in voltage versus engine rpm.
