Here is a simple template you can use to write an authorization letter for use of car.
Subject: Authorization for Use of Car
This is to inform you that [Authorized personnel’s name] has been authorized for the car’s use, the details of which are [Car model and number]. They have permission to use the car for [Period/Day]. They have also been equipped with the necessary documents associated with the car. He/she is a responsible and trusted individual.
[Full name of authorized personnel]
[Any identification number of authorized personnel]
[Contact information of authorized personnel]
In case of any complaints or queries, please contact me at [Your contact information]. Thank you for your efforts and consideration.