How do you use Flash on a Pokemon in the Granite Cave in Pokemon Ruby?

Question

I'm playing on a ROM actually

Answer 1

First, defeat Brawly at the Dewford Gym. You need the badge in order to use Flash. Then, go to the Hiker inside Granite Cave and he will give you the HM. (Thanks to Tysonyoshi for reminding me :D)
Go to the Menu which will appear at the right hand side. Then, click "Pokemon". Select the Pokemon that knows Flash, click on it and the following options will come up:

-Summary
-Flash
-Switch
-Item
-Cancel

Click Flash, and the Granite Cave will light up.

Comments

Wait did you mean how to make a Pokemon light the cave?

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Yeah, that's how you light a cave in a dark environment.

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Don't forget that you need to have the Gym Badge from Brawly too.

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Oh yep, thanks!