Use rock types like onix. they don't get hurt much by lightning. Water types suck against electricity
The third Gym Leader is Lt. Surge and you can find him in Vermilion City.
Celadon City and complete the events at the game corner.
you need to look in the trash cans. one of them might have a switch
The 7th gym leader in Pokemon yellow is in Cinnebar Island, which is south of Pallet Town. You need a Pokemon with Surf to get there.
'farfetch'd does not evolve' what? the third gym is in mauville. The leader is 'wattson' and he uses electric pokemon.
Wattson the electric gym.
MAUVILLE
Go east of Vermilion City until you find a cave, which should contain the Pokemon diglet. This Pokemon is a ground-type, which electric is useless against. With his Dig attack, it should be no problem winning in the third gym
The third gym leader is Lt. Surge, an electric Pokemon trainer. In the yellow version his only Pokemon is Raichu. Raichu can be easily defeated by a ground type Pokemon. Conveniently, Diglett's Cave is located right next to the town. In here you can find wild Diglett's and maybe wild Dugtrio's, the evolved form of Diglett. These Pokemon can easily defeat Lt. Surge with the Dig attack.
Go in. Beat the GYM. THAT SIMPLE
you beat the gym leader
You have to beat the 2nd gym.