The electrifier is a difficult evolutionary item that you will need to find in Pokémon Brilliant Diamond and Brilliant Pearl. Like many others, there are only a handful of ways to obtain the item, and you'll need them if you want to evolve specific Pokémon in their final evolutions, namely Electabuzz into Electivire. Here's what you need to know about where to find the energizer in Pokémon Brilliant Diamond and Brilliant Pearl.
You will be able to find Electirize by catching a wild Elekid. Elekid is the early evolution of Electabuzz, which is quite fitting because Electabuzz is the Pokémon that needs Electirizer to become Electivire. However, you won't be able to find Elekid around any of the routes.
Instead, you'll have to search the Grand Underground. We were able to locate him before he takes on Wake, then anytime after defeating the third Gym Leader, Maylene. You will need to explore the Grand Underground quite a bit, or just for a short while, depending on your luck. You should see Elekid around. When you get it, there's a chance it has the Electirizer on top. You may need to acquire more than one to make sure you find one that has it.