My charge controller shows red when battery is charged

Any brand/model information about your charge controller?

For the most part, smaller/less expensive charge controllers are not field repairable.

If the controller's LED worked opposite (say green when battery was low, red when battery was charged), there was one popular controller from Morningstar where the LED fell out and the user plugged it in backwards--All he had to do was rotate it 180 degrees to work correctly.

One other thing--Many solar charge controllers need you to connect to the battery first (and the battery needs to be near its rated voltage, not below 10 volts or over 17 volts for a 12 volt battery), then connect the solar panel array. If you connect the panel first, then the battery bank second, sometimes the charge controller will auto select the wrong battery voltage.

-Bill

There are hundreds, if not thousands, of PWM solar charge controller brands/models out there... Few of them are repairable.

Did it ever work correctly? Or is this a new install? Did you try 1. disconnect solar array to charge controller, 2. disconnect battery connection to charge controller, 3. wait a couple minutes, 4. connect charge controller to battery, 5. connect solar array to charge controller?

What is the voltage reading of the battery bank right now?

-Bill