‘Down to the wire’ – means, whatever is being discussed the result will be decided at the last instant or the last possible opportunity. it won’t be decided until the very last moment.
This idea isn’t working. We’re going to have to go ‘back to the drawing board‘.
‘Back to the drawing board’ – means, when trying something out and it doesn’t work or it does not have the expected outcome, you are going to have to go back to the beginning and start again and think up a new idea or another idea.
Drawing board is where a designer starts with an idea and makes it into a plan. Hence the meaning of the phrase.