My husband and I just swapped out all our external light…

Do you have an electrical tester?

What is that indicating at each in the lights?

Hold this next to both the black then the white wires at each light.

Yes, and the switch is on.

Yes, and the switch is on.

I can't see where you have the black wire connected to the other two lights. You will have to remove the mounting plate on these lights.

Yes.

You can leave the wires connected. Just slide the plate down and pull the wires out of the junction box so I can see the connections.

I need to see where you connected the black and white wires from the light to the junction box wires.

I think you will find that if you flip the power on and insert the tester deep into these two junction boxes one will signal power (red).

If that's the case that would be the one to open up and check the connections on first.

The daisy chain connections are made behind the original bracket. That's where you will find the loose connection. (if you have one here)

Hmmm. Try going to the switch and removing the trim plate. Test the two side terminal screws of the switch. One should always have power, the other should have power on/off with the switch.

Let's just make sure that the switch is working before you dig further into the wall.

These non-contact testers are not the best for troubleshooting.

Is this a motion sensor?

You need to remove the switch and test the wire to be sure that you are getting power out of the switch.

Where the old lights standard light build type?

No, red means power. Also these testers need to be close to the wire.

Hold the heater next to a working outlet to see the proper reaction.

Yes. But that doesn't mean it is working.

Are the new lights LED?

Insert the tester fully into the other side of the plug.

Also, try holding the tester alongside both sides of the white power cord from the outlet.

It has to be very close to power to detect it.

I have a feeling that the switch is the problem.

It may not be compatible with LED lights.

It's a very common problem.

If the switch was not designed for LED bildpbs it won't work with them.

Then we're back to the these fixture boxes. Without a multimeter (more accurate tester) you will need to open these up to gain access to the wires in the back.

Even with a multimeter, it may just prove that you have no power at the light and you will have to do that anyway and you will have to sort out why.

It could mean any several things. Unfortunately, the power in this circuit involves getting to the splices in the back of those two light fixtures. It takes a bit of detective work.

Tracing the power in this circuit will involve testing the splices in these boxes.

That's hard to say. It will depend entirely on how long it takes.

Although I can't imagine it will be a very involved task as it only affects a single light string.

OK, feel free to return if you need further assistance.