Those of you having issues with ELS no working / displaying etc with certain downloaded vehicles. I may have a solution as it worked for me on two different downloaded models for me. Basically I replaced the models in all gta folders and not just the mods folder.
I had the 2016 Ford Interceptor pack by the hurk. It wouldn't work. So I opened OpenIV and used "Tools" then "Search" and searched for the model files in the GTA folders, and replaced them all with the hurks model. I first backed them up to a separate file. The files were police3 (police3.yft, police3.ytd, and police3_hi.yft). This worked. I do notice the slicktop version had some lighting issues so I used the marked one instead and its fine.
I then tested this on another model. The 2015 Dodge Charger by Mr Potato. He used police2. So I used OpenIV again to search all version of that and replace them all (the 3 file - yft, ytd, and hi.yft).
Not knowledgeable enough to know why this worked but lets see if it works for other.