what would happen if you messed up and hooked up your black as your positive and red as your negative?
Do you mean at the battery? If you put the positive terminal on the negative post and the negative termina on the positive post you would (depending on the vehicle) do a combination of the following: Blow fuses, burn wires and destroy your alternator. You can plan on needing a new alternator, wiring harness and replacing fuses if you do this.
also when you hook your speakers to your box before securing you should always test to make sure you have your connections right also, this can be done with a double a (aa) battery ook the wire to the terminals on the right sides you think, then from the outside of te box connect yer wires and then take the battery, and touch the pos wire to the pos side and neg to neg side, if the speaker then pops out then the wiring is correct in there is something wrong, also, "do not old the wires on the battery for more then a second as it will cause damage to the v/c if you hold it there.
"batterys have different size posts like a wall outlet has a bigger slot on one side"