Don't work flashers on police cars after installing mods on the car (Grand Theft Auto 5)

don't work flashers on police cars after installing mods on the car, the first time I changed the police car's siren was not working, the second the car was put now on the contrary, do not operate the emergency lights and siren are removed the machine completely but did not help. Reinstalled the game, all the rules only to put the PACK with the cars and all the same, but this has not happened before