Adazca

What I first do when I import a lightbar is open all the parents and delete any L1s. (You can use the L1s that the lightbar gives you but I'm doing this to show you how to do it if a lightbar doesn't have L1s)

So the L1s are all deleted.

So now that we have the L1s deleted, we can do Select>Quadr and make sure you have Selected mode ON and select the whole lightbar. Then go up to Create>Copy and copy the lightbar. Now a second lightbar will pop up.

What you want to do with the second lightbar is open all the parents and rename all the L0s to L1s.

Now you want to move all the childs we renamed to L1 and move them up into the first lightbar we had. Now you have to select the lightbar again because if you don't the first lightbar will only move and the second won't. Then you can move your lightbar to where ever you wish.

 
Hope this helped!

Its the exact same setup regardless if you made the lightbar or someone else did. Make a copy of it and rename it with L1 on the end like Forward explained. 
 
Just a tip, for the L1's remove any small details to save polys and keep the size as low as possible. You don't need to see screws or small details for the L1's because your going to be at a distance where that stuff isn't necessary.

just copy the L0, and rename the L0 part to L1. problem fixed

I believe the problem is that you've not moved the _L1 and _L2 things to the same place as the _L0. There are two things you could do: 1. You could delete the lightbar's _L1 and _L2 however that's not recommended as there will be no lightbar on the car at "semi-far distances" and 2. You could move the _L1 and _L2 to roughly the same place as the _L0. This is the recommended option, but either will work fine.