Quick question
 

Im installing my new components in my door right now, on the cross over it says 0, +2 and +4.

Whats the difference and what should I set it too?

Thanks.

The +2db and +4db are attenuation settings. They can affect the way your tweeter sounds (brighter, etc.). You should try them out and see which one you like the most. I personally like a bright tweeter so I've set mine to +3db.

my mistake, its actually negative 2 and 4

Same difference.

The only way to correctly answer this is for you to hook it up in the car and listen, your car may be reflective and the tweeter may be too bright (I have my tweeters at -6 at the crossover)