93 Civic brake light problem

93 Civic 4 door driver side brake light is not working. I checked the bulb and swapped it with the one on the passenger side, the bulb is fine. This is a double filament bulb. One is the tail light (1) and the other is for the brake.

During day time , or when the headlight is OFF : Apply the brake => the tail light (filament) lit up, which is incorrect and also not bright enough.

Night time, or when the headlight is ON : Apply the brake => the tail light (1) which was ON , goes OFF. Result => no tail or brake light.

Wiring was not touch and looks fine. Where is the short and what can be the cause ? Can someone point out the possible cause ?