We tried to connect outside light bulp (AC) to a switch where an another light bulb is already connected. We did a parallel connection. Roughly like in the schematic. (I'm not an engineer so the schematic can be wrong).
simulate this circuit – Schematic created using CircuitLab
If I understand it right it should work like this: When the inside light is ON the outside light should be also ON. Because both lights are connected to the same switch. Or If I understand it right the outside light should light all the time.
But the lights work like so: When outside light is ON the inside light is OFF and vice versa.