I purchased an LED light display to help me orient my drone, but the package came with no instructions and I can't find any type of schematic that shows which of the battery posts in the P3S is positive or negative....can someone verify for me please?

Thank you!

Just put a meter on the battery,  it will tell you what terminals are what.  But ,  respectfully,  I suggest that the fact you did not do this indicates that this modification is not one you should do yourself.  You need to know what voltage requirements are for your lights,  how much current they will draw,  etc.  It is a little technical and not for everyone.  And could possibly result in fire or destruction of your drone  or worse .  Again,  not trying to insult you,  just making an observation.

Agree with Kneepuck.  If you don't know anything about electronics, you shouldn't be doing it.  There are decisions to be made, based on several things, and modifications that may be necessary for it to work right and be safe.

Thank you for the feedback. I assumed the connection should be pretty simple since this was an LED kit sold by Best Buy and geared for the Phantom 3 series.