I know according to the rules that an obstacle needs to be resolved before continuing to explore the room.

But what about power failure when someone has a lantern? The lantern ignores the darkness marker so I'm not sure why it would be so important to the investigator to solve the wiring puzzle before exploring the room. But that is probably just the roleplayer in me (I'm pretty new to being a Keeper/GM, I'm usually a player) If it ever comes up again I'll probably just tell them that the light from the antern is casting a lot of shadows and it is making it hard to find anything of use.

Yes, were the setting more modern, we could have an electronic panel hiding something, but possibly not so suitable for 1920s. For those with laterns, they aren't affcected by the darkness token if any skill checks come up, but yes, I believe there needs to be some reason for why they still have the effect of the obstacle card.

well depending on the room it could be that the items are in some machinary that isnt noticable unless its turned on. Or if its in the opertaing room, a person normally wouldnt inspect the inside of a body unless something glinted just right to catch their eye and the extra lights help or you need power tools to "operate"