Have any of you ever seen this? And if so, can you give me an explanation?
This is a typical box that would be used to trim around a wall opening or electrical box for vinyl siding.
Whats really weird is that the base plate is put on backwards. If you peak inside the holes, you will see the bare sheeting as well as some electrical wires.
(5 year old house. Seller didn’t have a clue either.)
lol. Yeah, it is basically a decorative backplate for an outside light fixture. It is so the typical round base is not straddling a couple of laps in the siding.
If you look closely, you can see where you need to score the plastic pad for an octogon box. Installed some on my own house. Real nice for a light fixture. 
Yea, they look great when they are used properly.
I can’t figure out the purpose… Hiding electrical wires.
BTW, there were two of these. One on either side of the house. One was really close to the AC shutoff, and the other was about 2 feet from the gas meter.
The electricians never made it back to the house to finish these after they stubbed out some wire and the siders finished. Depending on location, they probably were for receptacles.
That’s kind of what I was thinking, but they were on other houses in the sub., and where in a strange location for receptacles or lights. There were other lights and receptacles in normal places that were in appropriate locations. What would they have stubbed out 5 years ago that were never installed. Like I said, one was on one side of the house about 2 feet from the AC shutoff. The other was about 2 feet from the gas meter.
The sidewallers might have put them there to mount the AC disco’s on, but the electrician didn’t take the hint. Just a guess. They’re a J-block, but if there’s nothing behind them, it’s just a guess what it might have been intended for.
I am with Larry on this one. It is a universal trim box that was not used due to miscommunication or lack of returning workers.
There were wires inside. I couldn’t tell if they were in a J-box or not or if they were capped/cut or anything. I could just barely see them, and the sheeting behind.
Here’s some wider angle pics that give a better perspective on their locations.
Judging from the locations, I would say it was intended for outside receptacles that just never got installed. When working on an HVAC outside unit it is nice to have electrical power right there withing reach for running some tools, equipment.
These were a bit more obvious. They have been there 12 years.
Larry’s assessment is correct. Here are a couple of photos of the same receptacle or light fixture pad for vinyl siding.
This is the way that the installers leave it. The cover is scored for knockouts using either a rectangular box case an octogon box.
The pad is made to remove the cover and install a pancake octogon box, for this case a wall fixture for an outside light.
Hope this helps. 
I’m with Larry and Doug on this one Mark…just need the electrician back for the outside receptacles…jim
and, what is with the green sealer that appears to be a crack in the foundation?
epoxy injection
Looks like it may be for a disconnect. Looking at the picture the size looks about right and you said it was near the A/C.