Wait, do not buy the upper case. You could find a new replacement keyboard on eBay with the backlight for around $80. You do the math $80 to $250 for a non back light upper case. Just follow the instruction and you'll do fine.
If you just want to add a backlit just follow the teardown steps. Once you done the teardown your only adding two more steps.
Step 1 you'll be seeing the back of the keyboard which is cover in a black film seal with some adhesive. well there a black bracket on the center of it which supports the superdrive and the logic board. Now to remove it there's only two screws one on top and one on bottom of the bracket.
Step 2 remove the black film carefully, the edges are the only ones with adhesive. Once that's done you'll see a clear plastic underneath that is the keyboard component, but you don't have touch any of that in less your planning to replace the keyboard. If so, follow the next flew Steps***.
Now to install the backlit it replaces the black film. Make sure that the backlit ribbon is to the right of the keyboard ribbon, which is going to be the way you'll connect them to the logic board.
Also make sure you press down on the adhesive edges, that's the last defense you have from a water spill.
Then reassemble your MB/MBP.
If you just want a backlit for A1278 you could find it on eBay or even here on ifixit. Or even if your planning to replace both the keyboard and back lit.
Good luck with that.
***Step 3 Remove the clear plastic set it aside with the black film.
Step 4 There's going to be 6 row of 8 screws each that you'll have to remove. Be careful, if you strip one you'll have to drill the head off so you could remove keyboard. So when doing this Step take your time and use the correct screw driver phil#00.
Step 5 On the top left corner the power buttom ribbon there. You'll have to remove two screws.
Once you've done that, you could lift the keyboard out and replace it. Make sure that you put the clear plastic back. Instead of putting the black film back the backlit will replace that. Do make sure that you press down on that adhesive strip. That's your last defense encase of a water spill. Now reassemble the MB/MBP.
Hope that helps. Good luck with that.