Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
What is the year make and model of it?
You will want to be sure that there is power at the alternator at all times, (big red wire)
Unfortunatly the voltage regulator is built into the PCM, (powertrain control module) and if the fuse links are good, (power at the alternator) then the PCM would be the most likely problem. Or the alternator could be bad. You will want to test the charging system.
Of course, you will want to make sure that the alternator is grounded well also.
The Electronic Voltage Regulator (EVR) is not a separate component. It is actually a voltage regulating circuit located within the Powertrain Control Module (PCM). The EVR is not serviced separately. If replacement is necessary, the PCM must be replaced.The amount of DC current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series with the generators second rotor field terminal and its ground.
Was the battery light on before the alternator was replaced?
Do you know that it is charging?
It sounds like someone is not diagnosing it correctly. Or there is a problem with the PCM.
ON-BOARD DIAGNOSTIC SYSTEM The Powertrain Control Module (PCM) monitors critical input and output circuits of the charging system, making sure they are operational. A Diagnostic Trouble Code (DTC) is assigned to each input and output circuit monitored by the OBD system. Some circuits are checked continuously and some are checked only under certain conditions.If the OBD system senses that a monitored circuit is bad, it will put a DTC into electronic memory. The DTC will stay in electronic memory as long as the circuit continues to be bad. The PCM is programmed to clear the memory after 40 good trip if the problem does not occur again.DIAGNOSTIC TROUBLE CODES A DTC description can be read using the DRBIII(R) scan tool.A DTC does not identify which component in a circuit is bad. Thus, a DTC should be treated as a symptom, not as the cause for the problem. In some cases, because of the design of the diagnostic test procedure, a DTC can be the reason for another DTC to be set. Therefore, it is important that the test procedures be followed in sequence, to understand what caused a DTC to be set.ERASING DIAGNOSTIC TROUBLE CODES The DRBIII(R) Scan Tool must be used to erase a DTC.The following procedures may be used to diagnose the charging system if:
Remember that an undercharged battery is often caused by:
INSPECTION The Powertrain Control Module (PCM) monitors critical input and output circuits of the charging system, making sure they are operational. A Diagnostic Trouble Code (DTC) is assigned to each input and output circuit monitored by the On-Board Diagnostic (OBD) system. Some charging system circuits are checked continuously, and some are checked only under certain conditions.This will include a complete list of DTC's including DTC's for the charging system.To perform a complete test of the charging system, refer to the appropriate Powertrain Diagnostic Procedures the DRBIII(R) scan tool. Perform the following inspections before attaching the scan tool.