PO320 Fault Code on 2005 Kia Sedona: Ignition Speed Sensor Issue & Battery Light Persistence

I recently encountered a PO320 fault code on my 2005 Kia Sedona. The check engine light, along with brake and battery warning lights, remain illuminated despite replacing the battery and having the vehicle re-coded. The original diagnostic indicated an 'ignition/speed input circuit' issue (code 1/2), which I have now addressed by installing a new ignition speed sensor. After this repair, both the tachometer and cruise control functions are working properly — the check engine light has turned off, which is a positive sign. However, the brake and battery warning lights persist and the vehicle continues to drain power unexpectedly. I've inspected all connections and found only one loose connection: the overdrive plug, which was previously unplugged to prevent further battery drainage. When reconnected, the warning lights did not turn off. I'm now trying to determine when exactly the PO320 code was triggered — was it related to a sensor failure or could an alternator issue be causing this? The alternator would typically produce different fault codes (like P0161 or P0565), but I want to confirm whether it's still possible that a failing alternator is contributing to the battery drain and warning lights. I'm looking for cost-effective troubleshooting steps before investing in expensive repairs. Any advice on what to check next — such as sensor wiring, ground connections, or alternator output? Thank you for any insights from owners of 2005 Kia Sedona with similar issues.