Check engine lights all turned on at once

[JDemi]

Hey guys, I recently bought a 1998 outback!

After having the car for a couple of weeks I was looking at the fuse box and noticed a few wires were disconnected. I followed them up to the security sensor and because it wasn't connected to anything I just took it out and put it away in my garage. but, as I was sitting under the dash board I noticed there was a green connector both male and female that wasn't connected, I was curious to see what it was so I connected them, not thinking it would hurt. A couple hours late I decided to run over to pep-boys to pick up a few fuses and when i turned the car on my check engine light came on! since I was at pep-boys, I asked them to check my codes since they do it for free, after he plugged the code reader in 11 codes popped up! they were things like engine misfire, o2 sensor, feul, speed sensor (which works). 

As I got home feeling overwhelmed I remembered that green plug I had just connected earlier that day. I once again went under and connected it and low and behold the check engine light turned off. I plugged it back it and it came back on! 

I Need help!! why does this wire do that?? 

one other thing, the mechanic said it could be a bad ground wire because my turn signal lights blink fast and are dim, I don't know if that has anything to do with it.