Water damage/ replaced top case/ worked 1 time & burned out again

I purchased a 2013 MacBook Air that wasn't turning on, water damage. After reading through the forums I decided that replacing the top case was best. I purchased one off eBay, and it worked! Fired right up with the power button! Only problem is, it only did it the one time! Now the new top case has the same problem! What is next in line? What could be causing the power button circuitry to fizzle out on first go? I surely don't want to buy and replace the top case again until I'm certain it's not going to burn it out again!?!?! Helllppp!