Q: Voltage regulator smoking after replacement.

Hello, You should check the integrity of the ground wire. If the rubber coating is melted it must be replaced. You should be sure that the alternator they gave you doesn’t have a voltage regulator built in or attached to it. If the alternator is the correct one, disconnect the alternator completely, plug in the regulator, connect the battery and turn the key on and see if you get the same result. If you get the same result the regulator is faulty. If you don’t get the same result, disconnect the battery, connect the alternator, connect the battery and see what the result is. If it starts to smoke again and the alternator is faulty, return the parts and get replacements. You might need the aid of a mechanic, such as one from YourMechanic, to check for damage wiring, perform wiring repairs and diagnosis as needed.