Do you want to transform a civilian vehicle into a police vehicle? With this method you can do it very simply and quickly, just recover the flashing lights and attach them to your car then correctly install the vehicle on OpenIV.
You will need your vehicle found on modding sites or a vehicle from the game and a police vehicle.
Be sure to replace the police vehicle in the game with the one you took the flashing light bar from, if you take the one from police3, replace police3, same for police2...etc.
The only exception is that the police2 (buffalo) bar can be used on any vehicle in the game, so you can replace for example the Adder and have the flashing lights working, but you won't have the siren.
Don't forget to add the beacon textures to your .YTD.