What causes the charger light to shutoff while assembling the MacBook?

I am repairing a Macbook for someone who spilled a bit of water on it. We've replaced the keyboard and motherboard (bought from iFixIt) and I've been able to get the machine to turn on once, it booted through to the login screen and it stayed on until I turned it off.

About 5 minutes later I tried to turn it on again, and I couldn't get a single light or chime, I tried resetting PRAM, SMC, anything I could think of. Then I noticed the charger light wasn't even on. So I open up the macbook to make sure I plugged in the MagSafe board, I mistakenly left the charger plugged in and after I had unplugged the Speaker, CD drive, HD, essentially everything on the left half of the motherboard, the MagSafe light turned on again.

I finished stripping the machine apart to ensure I had plugged the MagSafe board into the logic board, and out of curiousity I left the charger plugged in (w/ a green light) as I began plugging things back in. When I plugged the HD in the light turns off.

My first thought is maybe that cables just messed up somehow so I check the others, one by one, and they all cause the light to turn off. We have spare cables lying around that I've tried with the same results.

I removed all the problem devices, ensured the charger light was on and for some reason had the idea of pressing down on the board lightly with a plastic stylus, and the light would turn off.

I have no idea what is causing this, and can't really confirm if it has anything to do with the Macbook not turning on again but it's the only sign I have that the Macbook is doing anything. Any help would be appreciated.