GM-GMC: 97 Astro charging system, alternater, ohm meter

Question
QUESTION: My alternator was making noise, so I replaced it. However, with the new alternator in place, the headlights start getting dim, and the car eventually stops running. I had the battery bench tested and it is good. I also had the new alternator bench tested, just in case there was a problem with it. The alternator tested o.k. I have a two terminal plug that connects to the alternator, but the alternator has a 4 terminal socket. Some sources I have looked at shoe a two wire plug, and some show a 4 wire plug, but the only alternator I have been able to find for that vehicle has the four terminal socket. The plug fits on the two middle prongs, but the car is not being charged. I pulled out fuses one by one and cheked the fuse sockets with an ohm meter. The ECU-I fuse, the IGN-E fuse, and the ENG-I fuse showed continuity; possible electrical short? Any ideas?

ANSWER: ok well the problem is the alternater you need a 2 wire alternater as the 4 wire needs the 2 other wires persent for it to properly charge. as one of the wires the connector isnt connected is the sensing terminal wich is where the alternater senses battery voltage to know when to stop charging the battery. as it is an open circuit the alternater senses max output of 14v and stops charging. so you might want to check what month the car was made if it was a late model after june then try the next year alternater if its a early model try the year before.

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QUESTION: The two years prior and the two years after all take the same alternator. Do you think that there may be an adapter from the two wire to four wire that may be missing? I could not find any listings of such an adapter, but thought it might be a possibility.

Answer
no there is not, its the internal design that determines how many wires that connect to it. there is no way to addapt to it as you have to have the all wires on a 4 plug connector correctly connected. the only thing i can think of is someone did an engine swap and that is not the same motor that was factory. and they also did a wire harness in it. or theres annother engine size option. so you might want to try to check other engine size options.