4-way with a 4th junction box?

This is a drawing of my boxes in my hallway. I’m including a junction box found also in the hallway because in the 3 switch boxes, there is only one box with a line/load romex but not a 2nd line/load romex unless I include the junction box. I’m wondering if someone can tell which is the line and load, and then which box I should install the smart switch. Thanks.20200217_140900|690x388

Should go in the box just to the left of junction box. Based of tracing your drawing out.

Your line should be the black that is in the Rolex bundle with neutral. The other two should be your travelers.

Its impossible to be sure but I believe the load and line are entering on the 2 wire Romex on the far left or in the junction box.

Unless you have a meter that can measure 120 VAC I would suggest you purchase one of these
or these

They are actually better than a meter in this case as you don’t need 3 hands.

Measure the black wire to the bare wire on the far left, switch the switch if the power remains on the black its likely you input power.

You can verify it by doing the same in the junction box.
One black will have power all the time, the other black (load) will go on and off with the switches.


Thank you both. I’ll verify line by measuring both ends and report back.

BTW I suggested you measure from what you think are line wires to safety ground. The reason I do that is if you measure from a line to a different line (not likely but possible) the voltage will be 0V or 220V. If 220V I’m sure you will stay clear of that wire but if they read 0 you might be in for a shock.