hello. The charging system is fairly straight forward. There are two electrical parts of the charging system. Lets call them power and control. The power side consists of the alternator output terminal, the wiring to the the starter "B+" and the wiring to the positive battery terminal. The ground for the alternator is provided by the connection to the engine.
The control side has two wires, One runs straight to the engine computer and the other is supplied 12v when the engine is running. The computer provides the ground circuit for the control side. The common problems are ( not in order of failures) , broken wiring at control side of alternator, thats the two wires that plug in. The engine computer failure. Battery connections at the starter post or the battery cable to clamp connection.
One way to test the system is to use a test light. There has to be 12 volts-Bright light - at the large output power connection at the rear of the alternator.
The alternator case should provide ground when a test light thats connected to positive battery and touched to the alternator case.
The next place to test is the control circuit. The computer energizes 12v to the green with orange stripe wire when the engine is running. The test light should be bright when connected to this wire -with the engine running. The other wire - green -is grounded by the computer to provide the charging control. The test light will glow when its connected to the positive battery and the green wire at the small alternator connector.
You can also connect the test light to the GR/OR wire and the GR wire. This will glow when the engine is started.
A few notes: The computer needs to "sense " the alternator control circuit- before it will turn the control circuit on. Simply said, If the wires are broken or terminal loose- the computer may not energize the control circuit. When the test light is used to test the circuits, It has to be connected to the wiring before the car is started.. The computer will think the test light is the alternator and act normal.
The terminals of the alternator connector can be damaged if probed with the end of the test light. We use some stranded wire to engage and make the connection with the small terminals of the connector.
We normally find a broken wire right at the alternator connector. An easy way to check is to hold the connector and pull on each wire and check to see if it stretches. If it does then that wire is broken. The connector can be bought and replaced, and the terminal /wire connection can be repaired if your careful.
I hope this helps. If you need more help. please reply.