The voltage is regulated by the PCM(powertrain control module), which has an electronic voltage regulator built in. It controls the voltage thru a signal sent thru the dark green wire to the alternator
Ok, first, at the black with gry striped wire at the alternator, you need to check it for 13.5v or more with engine running. If present, then you will need to repair that wire between it and the battery, usually the fusible link in the wire near the battery.
If not, then check the dark green with orange striped wire for at least 10.5v. If not present, you will need to check that wire for a break in it between it and the ASD relay If wire is ok, replace the relay.
If at least 10.5v present, then you will need to check the dark green wire for 12v with engine running. If not present, then you will need to test this wire. Disconnect the battery. At the firewall near the battery is the PCM - see attached for location diagram.
Now, on the PCM there are 2 connectors - a 40 pin and a 80 pin. Disconnect the 40 pin connector and disconnect the connector to the alternator with dark green wire. On pin 8 of the PCM connector - see attached for pinout - place one voltmeter lead and place the other lead on the pin at the alternator connector for the dark green wire. With voltmeter on ohm setting, check for resistance. If missing, the wire is broken. Either trace wire and repair or run a new wire. If resistance is present, then the PCM has failed and will need to be replaced
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