When I put my headlights on,all of my interior light come on also?

I tried dimming the Dash lights,using the control on the lever,it dims the interior lights but doesn't switch them off.

can you turn it the other direction and turn on the interior lights.

Yes,if I turn it fully forward (towards the dash)it turns all interior lights on. I've tried turning it all the way back when the headlights are on,but it only dims them...it won't turn them off completely?

I would suspect the switch is bad.