I suspect that the red wire goes to the hot input for the pathway lights that now don't work at all. First, check the red wire at the sensor and confirm it does not have AC voltage present when disconnected, then pull the nearest light to the sensor and I bet you'll find the other end of that red wire. A quick continuity test will confirm that.

That being the case, just wire that red line in with the sensor's output and they'll light up just like they used to.

Now, that all changes if you have AC present on that red line with it disconnected, because then they ran 220v to it for who knows why. I strongly suspect they just ran the 220 wire because they intended to use the 4th leg as a separate switched circuit kind of thing, but still on 110v

So the current sensor doesn’t have a red wire which is why my brother capped it off. I’m assuming replacing the sensor with a 3-wire sensor would re-enable the pathway lights by reconnecting the red wire but they will only light up when this sensor detects someone in the driveway heading to the gate. Is there a way to make the pathway light up when someone at the gate heads for the driveway?

Can't tell you that without a diagram or putting eyeballs on it myself. I was having a hard time following your description as it was.

I’m not exactly following without diagrams but you can purchase a motion sensor and wire it into any light or set of lights. With the right planning and access you could place a motion sensor somewhere and have the lights elsewhere, providing they are still wired together.

My guess is the "red wire" on the new fixture is internal. The black and white go inside to the wiring for the sensor and the sensor goes right to the light internally. There is a chance if you took ot apart you might be able to rig it but maybe not.

Google 3-wire light sensor diagram, then google 2-wire light sensor diagram. See what each goes to and figure it out yourself. Would have been faster than this essay you wrote.

I did that first but none of the results fit this scenario. I'm not trying to put a 2-wire sensor on a 3-wire outlet/fixture -- that's what's in place now. However, capping the red wire in the outlet/fixture has disabled the path lights and gate light and I'm trying to re-enable them, as well as seeing if I can set the path lights up to come on when someone comes out of the gate to head back to the driveway.

Had to open Reddit in browser on laptop since the iOS app didn't let me attach pictures but I edited the main post to put a diagram in.

The guy up there who said the other line was the hot for what’s not turned on is most likely right. Post a picture of the sensor you bought or put up a link, it’d help

Just going to piggy back here cause I can’t reply to your original post for some reason.

The new fixture he bought doesn’t have an output for the sensor. You need a fixture with that output to get the rest of the lights to work again.

As for your other question. It depends. You’ll have to take the light off that you want to replace with a motion and check if it has the 3 wires in the box or not. If it does it will be white to white and fixture black to red with the black of the cables just passing through the box. If that’s what you see then you can add a motion there as well. If you only see the black and white then you can’t without some sort of wireless sensor that Im not sure exists.

Hope that helps.

It is really difficult to determine what is going on without using a voltage meter or photos. You really need to do further investigation before connecting any wires.

You need a multimeter before proceeding! You can get an inexpensive meter for less then $20.00.

Check for power between the black and white (should be 110 volts).

Check for power between red and white (no power or 110 volts??) If there is no power, there is a good chance that the wire is charged by the activation of the sensor. If the red is 110 volts then further investigation will need to be done. You will need to find out where the wire originated.

Check for power between the black and red. If it is 220 volts, then there is a separate breaker for the red wire. Just CAP the red wire until you are able to determine what it is for. I highly doubt it will be on a separate circuit (220 volts) for exterior lighting. The wattage is low for lighting. There could also be 110 volts or no voltage between red and black. 110 volts would indicate that a light is already connected to the red wire. No voltage would indicate that both red and black have power and are on the same busbar on the electrical panel OR the red wire is disconnected. If there is no voltage between red and black, check again between red and white. If there is 110 volts, then red is on the same busbar as black. They most likely would be on the same circuit.

Open up the other lights to determine if the red wire connects to that box. Check for power in the other boxes.

You should educate yourself on basic wiring by watching some YouTube videos. Find some videos on troubleshooting wiring.

This is what I suspect: Black wire (line)- hot 110 volts. White wire - common. If there is no power between the red and the white, then there is a good chance that when motion activates the sensor that charges the red wire (load). That powers the other lights.

Provided the red is the load: To install another sensor further on the branch circuit, connect the red to the black together. In this situation, if you connect red and black together, you should have constant power for the other lights. Then you can install motion sensors in the other locations.

Get a multimeter before connecting any wires together.

That “diagram” you drew doesn’t add much context without knowing what wires go where. Maybe post a picture of the original and new motion sensors with enough detail to identify the sensors, the wires and any information on the units, along with what wires are present and where they connected on the original.

As mentioned before, you need to do more investigation with a multimeter. The red wire (14/3) might go to a junction box and then power the other lights. Test for voltage and test for continuity. Watch YouTube videos on both topics.

Test continuity with a long wire. There are other ways, but for the purpose of brevity, here is one way to do it. https://youtu.be/YLA5u8BJrwg

As an electrician I can say u/Yummy-Beetle-Juice did you a solid and wrote out everything you need to do to solve your problem. If you can’t or don’t want to figure this out call an electrician they should have it sorted in about an hour.

I would recommend a non-contact voltage tester as well as a good understanding of the limitations of these devices.

Telling someone who can't figure out the disconnected wire feeds the lights that are no longer power on to get a multi meter and start proving on live circuits doesn't seem like a great idea.

While yes electrical safety is important, they already figured out how to swap the light without causing any problems, sticking a voltage probe to the same wires shouldn’t be difficult for them.

More than likely the old motion sensor was powered with black and white wire, and the red was a normally open switch that closes with the motion(turns on). The new sensor is just a normally open between the white and black wires. So you would take your input power black wire and attach that to the motion sensor black wire, and the output(path lights)black wires to the white wire. Then you would attach the input power white(neutral) to the path lights white wires. With this new motion sensor you are only switching the hot wires on/off with a motion switch no neutral(white wire) is needed to be attached to motion sensor for it to work.