My 1991 Miata headlights sometimes will not open at night? The headlights are on inside the hood.but will not come out..

My 1991 Miata headlights sometimes will not open up.  They are on under the hood but
will not come out. I have to sit at night and keep turning them on and off.  The parking
lights are on and the tail lights are on but they will not open for a while.  I get out tap them
lightly, nothing...I close the hood hoping that will help but nothing.  Finally when they feel
like it they open. But they are on under the hood all this time...