I've already removed, sanded the connections and retightened these.

I've checked all the fuses/relays and power connections and everything seems good. Only reason I was suspecting the BCM is because randomly the car drops all power (no dome light, no horn, nothing) and then randomly it comes online. The ECM/TCM fuses and relays are receiving power too. I might need to check all the grounds, I saw Don has a list of them posted on another thread.

Yes I removed the entire fusebox and retightened very very tight, I also removed the fuses/relays to make sure each one is getting power as well. I've tightened the BCM bolt, and 4 fusebox bolts. I have also removed, sanded and retightened the starter/alternator wire along with what I believe is the power steering wire that sits alone above the starter/alternator wires. I will check all grounds next.
RESPONSE

 

The smaller wire at the top of the pic is the power steering. There should be 2 wires connected under the red cover.

The fact that ALL power randomly stops says that the battery lugs are not tight. They are easy to break. If you can move them by hand they are too loose.
No start, no crank after a engine swap is almost always caused by the fuse box bolts being "tight". All of those connections need to click in.

 

Recheck routing for the starter cable and the alternator cable and the small wire on the starter is it on the correct post?

 

I'm not too sure where the timing chain/engine swap is coming from but I think you might be confusing it with another thread.
The owner just said it wouldn't start one day. He thought it could be theft or bcm, but after not being able to figure it out he gave it to me for free. Original engine, only 63k miles.
And yes, there is 1 single wire on the top (PS) and two wires under the red cover. I've checked both.