For anyone who may ever search this issue if you're dealing with the same thing:
The main issue : Getting ELS lights to activate on service vehicles that have light bars, but typically are not designed to light up (ex. towtruck, towtruck2, flatbed, speedo, addons)
The fix: Go into your carvariations file in Open IV (update/update.rpf./x64/data)
- On the vehicle that you want to place active lights on, add values to both the light and siren settings of that vehicle set. This is typically located at the end of each vehicle set. Each vehicle set closes with "</Item>", so you should see it slightly before that line.
<lightSettings value="15"/>
<sirenSettings value="16"/>
After changing these settings everything works and the service vehicles are now responding with code 3 lighting! To my knowledge there aren't specific values that you have to put, but if you put a siren value between 1-9 there's a chance you may hear the siren when they're responding and that's prob not the preference for a tow truck, to each their own tho.
Blessings to you all.