I briefly touched upon this in my GTA V FAQ's, but seeing as there are still some people not aware, lets have a dedicated topic. Emergency Lighting System (ELS) is meant to be used with ELS specific cars. These cars have been built around ELS and the features it provides. Fortunately, ELS also works for non ELS made cars in the most basic form - effectively turning ELS into a better Siren Mastery, or for those who don't know what that mod is, it gives you better control over your siren. ELS requires you give a car the VCF XML. This VCF allows for ELS to read and recognize the car as being made for it. All you need to do is rename the VCF to the name of your non ELS car, place it in your active ELS folder (pack_default is the default folder).
We're not done yet, there's some edits that need to be made first in order to have everything work smoothly. I will be provided a VCF that already has everything set and ready to go if you don't want to do any editing. Just rename it to the appropriate car, place it and you're ready. The VCF is attached at the bottom of this post - you can ignore everything else from here.
For those who want to learn and do some basic editing, open the VCF you want to edit.
1) Under "interface", you'll see LstgActivationType. Between the two tags is the word "manual". Delete that and put "auto" instead. What this means is that when you turn on your lights, it will turn on all of them, instead of turning them on in stages like you can with ELS cars.
2) Under <EOVERRIDE> you'll see multiple extras. Where it says IsElsControlled="true", change all of them to "false". Only change the IsElsControlled entry! This is pretty self explanatory, it tells ELS if it's controlling the lights or not.
In continuation of the siren control, there is a section called <SOUNDS> . Here, you can disable certain tones (AllowUse="false") if you don't want the car using them.
There is the <ACORONAS> section which lets you mess with wig wags, I'm not positive if that actually does anything for non ELS cars. I may try it later just to see, but I'm assuming it does give wigwags.
As many cars as you have in your game, you can have the same amount of VCFs. My game is full of ELS cars and I've yet to run into a VCF limit. You can edit the active ELS car limit in the ELS ini.
NON ELS VCF.xml