Mitsubishi Repair: 1991 Mirage electrical 1.5, correct tension, integraty

Question
1991 Mirage 1.5
Hi I have been fighting an electrical problem for over a month I have changed the alternator three times and am currently on my third battery. I have just put in the third new alternator and went to test the car, The lights and everything worked at first but then the lights go dim and shortly after the car dies. I have had the same result each time I have put in the alternator. I have checked that all wires are connected. I have a grond connection the plug with two wires, and the main wire. I have checked all the fuses in the car that I could find as a friend said a bad fuse could prevent the battery from charging. But even if the battery is not charging shoulddnt the alt. produce the power to run the car and lights as needed. Alt. tested good when pulled and bad when in the car. Hope you can point me in the correct direction for trouble shooting.
Thanks in advance

Answer
Carl,
Check the physical integraty of the cables going to the battery, alternator and starter.  Those typically carry the highest currents.  If the alternator was not making a good connection with the battery, or if the battery was not grounded properly (or poorly), the car will run erratically.  You may want to replace the ignition and alternator fuses just to be sure they are not the problem.  The alternator fuse can easily be blown when installing or removing the alternator.  Also be sure the alternator drive belt is at the correct tension.

Also be absolutely sure you have the polarities correct on the battery.  If the battery had ever been installed backwards, it could cause permanent damage to sensitive electronics in your car.  If need be, replace all battery cables and post connectors.  Any of these small items can cause the problems you're experiencing.
Good luck!