The 3rd Gym Badge in Pokemon Leaf Green is in Vermillion City. To get into the Gym You must have the HM Cut. Then cut down the small tree blocking your path to enter the Gym. Once you get inside, you must look in the trash cans for two switches. After clicking on the two switches, the electric borders to the Gym Leader will open. The Gym Leader, Lt. Surge, uses electric type Pokemon.
TIPS
1. Once you find the first switch the second will be right next to it.
2. It is possible to reach they Gym Leader without battling any trainers.
3. Lt. Surge's Pokemon are weak against Ground and Rock types.
EADGE
In Vermilion city.
vermillon city
Go defeat the 4th? :)
On cinnabar Island, to the left of the pokemon center, lies a "laboratory". If you go inside, then go to the right and enter the third door. Talk to the Professor there.
go to vermilion city and go to the boat on the third deck in a cabin
sail to one island and go into Pokemon center.talk to celio.thanks!
at the lab on cinnabar island the third door talk to the guy in the white lab suit
yes there is it's called Pokemon water blue
The third gym is located in Vermilion City it is placed below the Pokemon Center and there is a tree you can Cut nearby it which is the only way to enter it at this time.
You have to win all of the other gyms then go right into it and the doors are open
Go to Celeadon, go to the the GIANT pokemart. Head to the third floor, talk to the guy and buy a Firestone.