I want to make it so that when the player wears my modded armor the game will detect it and act accordingly. 

in older versions I believe you had to do this.

ItemStack helmet = this.getEquipmentInSlot(4);
if(helmet == mymod.myhelmet) {
//do this
}

but i believe it no longer works for 1.12.

You can try with this:

Minecraft.getMinecraft().player.getArmorInventoryList().contains(mymod.head)

 

Remember that getArmorInventoryList return an Iterable of ItemStack, not Item.

2 hours ago, J_Dev said:

ItemStack helmet = this.getEquipmentInSlot(4);
if(helmet == mymod.myhelmet) {
//do this
}

 

That if-statement will never be true, you're comparing an Item with an ItemStack which are completely different types.