Recently I converted 3 replace cars into addon cars. I pressed shift to initiate the traffic stop which worked, however I went to stage 3 ELS and I could not blip the AI to pull over. I have no clue how to fix this.

Make sure you've replaced all of the necessary data files for that addon vehicle, including carvariations.ymt. 

 

Your topic has been moved to GTA V Support, this is not LSPDFR related.
Please post in the correct location in the future.

With the addon converter I'm using it automatically makes the carvariations and meta files, what should the files say for it work properly?

2 hours ago, IlluminousInfinity said:

With the addon converter I'm using it automatically makes the carvariations and meta files, what should the files say for it work properly?

Your add on converter uses the civilian car meta files, which do not include the emergency vehicle flag, replace it with any police slot and rename your txt, game name, etc to the addon name, and change the handling to whatever you like

My addon car didn't come with any vehicles.meta files, should I add one?

1 hour ago, IlluminousInfinity said:

My addon car didn't come with any vehicles.meta files, should I add one?

Are you sure? Can I see the folder of the car?