Trouble wiring outside lights

[Paratus]

I'm trying to replace two outside lights. This is something I've done several times but I'm losing my mind on this. I have to lights side by side in parallel. I'll refer to the first spot as #1 (it's on the right) and then #2 (on the left) is where the line ends.

I had an old basic light on #2 yet #1 was empty. The light was removed a few months back, but it worked fine. If I hit the switch the old light on #2 would light up as expected.

I added a new light (has a light sensor) on #1. As soon as I did that, #2 would also not turn on anymore. I thought I messed up the wiring but black to black, white to white is pretty simple. When I took the new light off #2, #1 would turn on again! I'm no electrician but how does this make sense when it's parallel?!?!

I took the new light off #2 and put it on #1 because that one WOULD light up when nothing was on #1. It doesn't turn on.

I have 6 of the new lights, so I tried 2 others. 3 of 3 tried do the same thing. I tried different bulbs. What am I missing??

An expertly drawn wiring diagram is attached.

 

[littlespark]

Can we look at the wiring connections on each fitting, and the connection diagram in the instruction manual?

Are these both new sensor lights?
So turn on the switch, power is applied to sensor, then light only comes on when sensor is activated on each particular fitting?

Some of these sensor lights come on as a self-test mode when power is applied for a few seconds… then go off and revert to sensor mode.

 

[Paratus]

Can we look at the wiring connections on each fitting, and the connection diagram in the instruction manual?

Are these both new sensor lights?
So turn on the switch, power is applied to sensor, then light only comes on when sensor is activated on each particular fitting?

Some of these sensor lights come on as a self-test mode when power is applied for a few seconds… then go off and revert to sensor mode.

I've actually replaced the lights with more basic ones which don't have a sensor. I hooked them up, and they worked right away! But, then we turned off the switch and the lights never came back. It's the same thing. The lights are currently disconnected and I tested one of the sockets with a volt meter when it was turned on (again, no light connected, just the exposed wires). It showed 121 volts.

I'm completely at a loss here. Sometimes they work, sometimes they don't. It shows enough voltage? I have a basic understanding of residential wiring but clearly not enough to have any idea what is happening in this case.