I know there's already a thread on how to do this. I followed it as well, but for some damn reason 8 couldn't get it to stay properly with the 3M tape so i decided to take a different approach and take some pictures.
Easy part was taking the carpet down. I removed I think like 5 of them since it was dark out and about 36 degrees. I just held it down with my elbow while i removed the trunk light. I guess you could remove them all, but i didn't have an extra 32 seconds to spare. I'm too impatient. Unplug the connection, loosen the two 10mm nuts, pop the inner tabs right next to the bolts inwards and voila! It pops right out.
Next, pulling apart the simple assembly is more words than difficultly so I'm just going to skip over that. I used the tail light from an 01 Impala which I got off of ebay for $14. All you need is the circuit board and the rest you can throw out. Make sure you keep the pins from the + and - negative wires attached or else it can/will be a pain to connect to the factory harness.
Off of your cobalt's brake light, the black connecting piece with your 3 lamps you no longer need as well.
I took the reflector housing and drilled 5 holes. Ignore the duct tape on it. I used it for marking purposes since it was at night. One for the wires + and - out the side like so:
And then 4 more along the inside of the curves. 2 on each side:
Then I used 2 ty wraps to secure the circuit board in place. I pushed it all the way down to the bottom of the reflector housing to ensure that its straight/level:
After that I GENTLY tightened the ty wraps while I made sure the circuit board stayed in one place. I cut off the excess after it was next to impossible to move and put the red housing back on and headed outside to my car.
With those 2 pins that i stuck thru the side, i pushed them into the correct side. - was black obviously and the + was green for me. Just as a safety precaution i used some electrical tape to hold them in place in the connector.
Then you can put everything back together. Clips, nuts, and the tabs. One thing i noticed while putting it back together, make sure you look at it from the outside before you start tightening the nuts. The foam part was sticking out for me and I shifted it a bit to move it back into place. Just the little things I guess. All done. Easy right?
I think my trunk was open a little bit when I took the pictures but here it is all done:
Thanks goes out to CTCOBALTSSS for his How To which i followed first.