Like Gutch said, it works independently. I also did the test and now have 4 installed and it seems to be working really well. One seems to read a little high on the humidity but I have a hygrometer there now to cross check it in the case, may be worn out humidipaks.
If they left the ES 2 in the bridge and the board in the guitar with the wire and harness you should be all set.
Good luck,