This reminds me of an episode of Stargate SG-1. The team discovers an asteroid heading towards Earth, so they fly a Goa’uld cargo vessel to it, plant a nuke on it – only, they then discover that the asteroid is made of pure naquadah, and the explosion would obliterate Earth, so they need to defuse it. (Typical sneaky Goa’uld bastards.)

So, Jack O’Neill sets out to defuse the thing, and…

Carter (after finding out that the keypad is broken): “Sir, you’re going to have to open up the bomb and deactivate it manually.”
* O’Neill opens up the bomb
Carter: “Now find the wires running from the timer to the detonator, and cut the red one.”
O’Neill: “Carter, they’re all yellow!”
Carter: “Say again?”
O’Neill: “There are five wires, and they’re all yellow! Should I cut them all?”
Carter: “Thing is, if you interrupt the wrong circuit, it’s basically the same as telling the bomb that the timer has reached zero.”
O’Neill: “Yeah, I knew that.”
Carter: “I’m sorry sir, but you’re just going to have to cut them randomly.”
O’Neill: “Yeah, I knew that too.”
* O’Neill randomly cuts one wire, then a second, then a third. The bomb is still ticking.
Carter: “How’s it coming, sir?”
O’Neill: “I’ve cut three… there’s two to go.”
* A pause…
O’Neill: “You know, I’d like to take this opportunity to say that this is a very poorly designed bomb, and I think we should say something to someone when we get back!”
Carter: “I agree, sir.”
* O’Neill almost cuts one of the two remaining wires, but changes his mind at the last minute and cuts the other. The timer goes blank.