Where is 12V in the doors panel?

Hello im looking to find a 12V in my doors i want to wire retrofit Ambient set lights but i dont know where can i find a 12V when the engine is ON. i have old OEM ambient in my car but idk if there's 12V after i turn on the engine or is it only at night? because OEM Lights light up only at night so im not sure. ATM I wired the set to a cable from windows switch but idk why when i open or close doors the lights get turn off and i have to stop and start the engine again to light up :D