This tutorial only applies to vehicles with multiple extras.
Once we have the vehicle setup to our liking, we'll want to attach the extras together so ELS will actually work in-game.
First things first, check to see if the lighting equipment has any "helper" (or similar) folders within the main folder itself. As you can see, there are two helper folders here.
Drag these helper folders out of the main equipment folder (in this case WhelenEdge and Whelen_Talon) above the vehicle model (police.wft).
Once the helper folders are no longer inside the main equipment folder(s), proceed to delete the equipment folder(s) (this is not a requirement, but it keeps things tidy) by right clicking on the folder and selecting edit/delete.
Open up the helper folders, as you can see there are multiple extra 1 and extra 4 folders. These are what we will be attaching (only attach the extras if there is more than one set). At this point, decide which light bar will be the "main" one you will attach everything to. For this tutorial, I have selected the Whelen Edge (the second helper folder) as the main light bar.
Open the extra folders, inside you should see a extra_L0 file. Drag the extra_L0 files out of this folder and into the main light bar (WhelenEdge) extras folder.
You should now see duplicate extra_L0 files.
Right click on the main light bar folder (WhelenEdge) and select "Show isolated", this will hide all other layers/folders but the one selected.
The hierarchy and view panels should know look like this... and oh no! The car is gone! Don't worry, this is perfectly fine.
Now hide the main light bar base (the actual bar itself, not the extras - these should be named differently). You should end up with a view like this.
Under the tools tab on the left hand side of your screen, click on modify and then click attach.
Making sure Selective Mode is off (keyboard shortcut - space-bar), attach the extras to each other (extra_1_L0 to extra_1_L0 and extra_4_L0 to extra_4_L0, ect) by clicking on the secondary (talon) extras and selecting the primary (edge) extras.
The duplicate extra_L0 files should now disappear from your hierarchy. This means you have successfully attached the extras together.
Right click on the main light bar and click "show the rest". This should reveal all hidden layers/folders.
The extras folders (where you took the extra_L0 files from) can now be deleted (once again, this isn't required, but it keeps things neat and tidy).
If the vehicle has any sub folders inside the lighting equipment folders (as shown, there is a misc_g folder inside the talon helper folder), drag them out and delete the original folder. At this point, rename any folders that are named the same (in this case I've changed "helper" to edge).
Place the lighting equipment folders (edge and misc_g) inside the vehicle model hierarchy folder.
Because the lights are mounted on the roof and dash of this vehicle, they're fine to sit under the chassis_L2 file, however this is dependent on the lighting position (ex: if you have lights in the grill, they should go inside the "bonnet" folder. NOTE: Always make sure the extra_L0 files are above the lighting equipment model, such as the base/stand, itself!).
Hopefully this tutorial helped you. If you have any questions, please leave them below and I will try my best to answer them. :)