I can't be sure from the photo, but it appears that someone applied siding over the light's junction box. I don't know how the old fixture was fastened, but you should be able to install the new one with a strap screwed to the box - assuming it's there under the siding. If it's there, you'd need to trim the siding back carefully to expose the box. If it's significantly below the siding's surface, you may need to add a box extender. And if there's no box, you or an electrician should install one.

Is that the old light or the new one? If new, did it come with a mounting bracket?

Agree you should open the wall a bit more to find the box.

I’d like to know whether there is a box in the first place. More info is needed before we get to the answer of how to install this fixture to meet code.

In my original picture, the new fixture that I am holding on the left is the new one. I no longer have the old fixture. The old fixture was connected by a threaded thin tube that was connected to what I think is the original junction box.

Here is a better picture of what I think is the original junction box that's (I'm guessing) mostly buried behind the siding.

also there is a mounting bracket and some instructions.

thank you. The black S-shaped thing appears to be a dark green wire of some kind. There appears to be more holes in that metal bracket that is hiding behind the siding. I will try to gently expose it more, with breakers off.

Ok... we’ll get this resolved ;-)

The dark green wire is actually a bare ground wire that's corroded. No worries, it'll clean up.

Go ahead and enlarge the hole in the siding until you get to the edges of the box. Probably the easiest tool to use will be a pair of tin snips, or even fairly sturdy scissors. Once you have the entire box exposed, you'll see how your new mounting plate goes on. You'll need to remove the existing strap. You might have to coax the old screws out with a squirt of penetrating oil and a few light taps with a hammer.

I have extended the opening, and behind it there is a wall, made of what appears to be wood. A single metal bracket was affixed to that wall with two screws. The wiring goes into the deep hole in the wall.

So it looks like you need to install a box - eg.:
RACO 4 in. Octagon Box

But - to be honest - I'm having trouble following your photos - it's hard to tell what the construction of that wall is. In some it looks like there is a threaded hole that the old fixture mounted to using a threaded pipe and the wiring did not come through the hole - in others it looks like the electrical cable comes through the hole.

It looks like the old fixture strap was screwed directly to the original wood siding, just below the hole where the cable exits.

I have a rental house built in the late 1950s with 3 outdoor lights. Every one of them is installed that way - no box. I have a vague recollection that at one time the code allowed fixture canopies to serve as a box, but my memory chips are the old 16k 8-bit DIP type, and they might be starting to fail.

Ron, please correct me if this is wrong, but couldn't he install a pancake box there and meet code?

Thanks all! I got it all installed!

Nice job, better than it was before.

Glad you got it solved! It looks good, except that the extra bare ground wire should have been fastened to the pancake box itself with a dedicated grounding screw, rather than to the bracket. So it's not 100% to code. I wouldn't call it unsafe, though, and it's better than it was. You did wrap the ground wire the correct way (clockwise) around the screw you used.

Were the wire connectors that you used supplied with the light fixture?

Thank you!

I've been learning about wiring things properly but I don't know the code.

I will be installing a photocell on that light, so I will get another chance to I reconnect the ground wire. I got the wire connectors separately.

Dennis-

What you found was exactly what I was worried you would find, and it looks like you did a very workmanlike of making it right, including using a clamp where the cable enters the box. I agree with David that you should reattach the ground wire to the box; you should find that one of the holes at the back of the box is thread to accept a grounding screw.

Actually, there is a green ground screw in the box. Well, it looks kinda green, may be a shadow.

Did this used to be an outside wall, like a porch?

weedmeister, this is a porch light, yes. The screw you saw is not green, so it is likely a shadow. There is another screw that was supplied with the box, that has a strong green marking. It's not anywhere in the pictures. The reason I didn't use the green screw into the box the first time, is this - it's a thicker screw and there is a wooden wall right behind the box. I didn't have a drill-bit thick enough to create a hole for the screw to enter, so I attached the ground wire to the plate in the mean time.

You need to pre-drill the hole for the box grounding screw before mounting the box. At least that's how I do it. Maybe the pros just let the screw dent the wood.

If you really don't have a drill bit that big (1/4" is more than enough), you might as well buy a full set of drill bits the next time you're at the hardware store. Every homeowner should have a good quality set of at least 13 bits. In fact, get two sets, because someday you'll break or ruin a bit you desperately need when all the stores are closed.