Nissan Repair: Alternator Good, Electrical Drain, 1987 nissan stanza, nissan stanza wagon

Question
I have a 1987 Nissan Stanza Wagon. I've been having a recurring problem concerning a mysterious electrical drain for nearly a year, and my local Nissan dealer service can't find the cause of the problem.
Usually at night while I was driving on a highway, my car would gradually lose electrical power and come to a stop. The battery would be drained. I would need a battery recharging or new battery. A local service shop twice said that the alternator was working properly, but the problem persisted. They would charge up the battery, and the car would operate fine for about two months, and the same thing would happen. I bought a new battery, but the problem occurred again. I took the car to a Nissan dealer, and the first time they said the alternator was fine. They sold me a new battery. The problem reoccurred about two months later, at night on a busy highway. The next time the Nissan dealer replaced the alternator, after they said that the current alternator was not charging sufficiently. After 2 1/2 months, the problem reoccurred, and I was stranded on another busy highwat at night. As is apparent, the stopping occurs usually at night with the lights on and when I applied the brakes (brake lights). I suppose that applying the brakes at night with the headlights on drained the remaining electrical power in the battery. It would not be a sudden stop, because I would notice that the headlights and dash panel lights would gradually dim over an approximatly five minute period of driving. Might there be a bad cable or wire in the electrical system?

Answer
First I would check the output of the alternator.  If the alternator checks out correctly and puts atleast 14 volts I would be looking at a bad electrical connection at the alternator and the battery.  If the cables are in good order and there are no open circuits I would do an amp check to see how much amperage is being used when all the accessories are runniing that you describe in your post.  With the headlights on and the brake pedal depressed and the engine on what is the draw on the system?  If one of these things really drains the battery I would look at that circuit to see what is causing the abnomal drain.  Dealerships and shops want to be done with your vehicle and will do the fastest thing to resolve the problem.  If you are not savy with electrical systems you might think about taking it to a speciality shop that deals with electrical.