With the key on you should have 12 volts at the heavy red wire on the back of the alt. The smaller gauge wire with the snap on connecter is the field wire & it too should have 12 volts. If you have both the alternator is junk. My guess is the field wire is dead & so the next thing to check with the key still on is the volt light in the dash it should be lit if not press on the dash panel & see if it comes on. If busy fingers have been into the dash. The terminal at the rear of the speedo head may not be making contact with the printed circuit tape strip that feeds voltage to the instrument panel. The volt light is part of the circuit that excites the field to make the alt charge & must work. The other possibility is the fuse link at the starter could be broke or melted. Electrical problems are most often the result of careless handling of wires or improper installation of electrical gadgets. These cars are getting older & who knows how many experts have been into the wiring by now.
