Insure you do the resistance check as in the instructions between the alternator case and the negative battery terminal.
Just saw your location, dampness on an older car over time causes a lot of corrosion. The resistance check may find your problem. Most hand held meters are not very good at measuring low resistance, if you touch the meter leads together when you turn it on it should calibrate to take out the resistance of your meter leads.
It's possible to measure voltage from the alternator case to the output lead on the alternator when running, make sure to use jumper clips-don't hold your hand in there when the engine is running. If this reading is about 14V, your alternator is fine, you have a poor connection somewhere. Don't assume that metal to metal connections are good. The ground post on the battery has to have a really good path to the case of the alternator.