How do you know when it is the battery, alternator, starter or just a problem with the wiring. One of my customers said “I jump started the car, then pulled the positive cable off the battery. That’s how I knew it was the alternator.” Hmmm! That may have been an easy “shade tree” test before the computer was put in and technology has taken over. Not so easy on these new computer controlled vehicles.
The first thing you need to do is make sure the battery is ok and able to hold a charge. The local parts stores check and charge batteries for a minimal charge. When you install the battery make sure the terminals are clean and tight. There are some pads and sprays that help protect the terminals from acid corrosion. I highly recommend them. This should get the car started.
For the next few tests you would need a test light and voltmeter to verify voltage/voltage drop. There should be 12 volts to the big wire on the back of the alternator. If not this wire or connection needs to be repaired. The smaller wires are for field or ignition, some of them are grounded by the ECM (computer) or powered by the ignition switch. You would have to know what type of charging system is in your vehicle to test these wires properly. On one system the computer grounds the field wire to get the alternator to charge. On the other system the field wire is going straight to ground and the power is switched by the ignition, with the key on engine off 12 volts should be present and 0 volts with the key off. Some of the older vehicles have external voltage regulators that are a little complicated to check also.
The voltage drop test is a little more complicated if you are not familiar with a voltmeter. Test voltage at the battery post while cranking(the engine will need to be disabled by unplugging the coil primary, fuel pump fuse or relay).Then test voltage at the starter while cranking, positive to starter wire and negative to starter body. If the difference is more than 1 volt then you would need to test each connection (terminal to battery and wire to starter) by putting positive on wire and negative on bolt while cranking any more than .5 volt and that connection should be cleaned and tightened.
Well, I hope this helps to save a few bucks. It may take a little time but now in this economy some of us have a little more time than money.