get the hm waterfall (forgot were u get it) and go 2 the Pokemon league climb the waterfall and go in 2 victory road 2 the other side!
Hope i helped! : )
Head to lavaridge town for your next badge.
it is Mauville gym
Somewhere near Mauville
With the seventh badge in Pokemon Ruby version, you can control caught or traded Pokemon up to level 70.
You can get the 6th badge by defeating your father in petalburg.
Lavarage its in. ST4282
If you mean the third gym, then it is located in Mauville City. In which the gym leader is an electric type which can easily be defeated by a ground type pokemon.
Beat the Gym Leader
get it from this fisherman i think
At Sootopolis City.
Fortree City ( Feather Badge ) Leader's pokemon: Altaria, Swellow, Skarmory, Pelipper
The third badge is in Goldenrod City.