Automatik headlights /tail lights
 

I have 2 problems with 2 different Cars. The first car my headlights turn on when the ignition is on and the switch in off. But my tail lights doesn't always start automatically. On the second car neither the headlight or taillights starts . Is there a relay that controls this or where should I start looking for faults.

All lights work when I turn the light switch to on.