Moses... honestly.. please read carefully the manual .., install the last version of the manager (1.72) on your pc... connect the Cross Hair to the PC.. choose Project Cars (1) configuration...
Then setup/connect corrrectly Cross Hair on your ps4 with the DS4 and the G27 connected.. (before starting PS4) and then connect PS4 pressing the start button n ps4 (nos using the PS botton on your DS4) .. and the you´ll be using mostly the G27 commands and only the PS button and the options button on your Ds4 ... and y´ll fingd that it works!!!!
Simply follow the manual carefully... and you´ll have no problems with this game, the Cross Hair ... , G27, and it´s compatibility to pratically every racing game on PS4 (Except for WRC 5 & 6 and probably 7, where you have to use 2!!! Ds4s!!!)
Good luck, dude!