Just did a fresh install of GTA at a final attempt to fix this issue, but it still persists. Carefully installed ELS to make sure it was done properly, and downloaded a simple 2019 charger in police2 slot. Placed the META and vehicle files in their respective spots in OpenIV, and placed the xml in pack_default in the directory. Also installed Scripthook and ScripthookNET, as well as uninstalled/reinstalled ASI manager stuff.
The problem I have (and every ELS car I install) is when they are spawned or being driven by AI, any emergency light on the vehicle is stuck in the ON position, no flashing, no option to turn them off. ELS staging does not work either (yes I checked Scroll Lock). When using a controller, the only thing I can get when pressing the right stick is wig-wag tail lights.
I changed visualsettings.dat to 1200 day and 900 night. The lights are perfectly bright, but not flashing or turning off, as well as no staging options.