Go to the following URL: http://www.google.com/local/add/lookup?hl=en-US&gl=US
The form presented at this URL will ask you for information regarding your dealership, like address, phone number, hours of operation, types of payment you accept and a description of your products and services.
You will then be asked to select the business categories that fit your dealership. You should type in "Automobiles" and Google will list several recommendations.
Go ahead and select "Browse all categories" (after your "Automobiles" search) you can view all available categories. Scrolling down to "Retail Stores - Automobiles" will take you to the ones that are auto-related.
Select up to 5 categories that best suit what your dealership sells.
Google then allows you to enter additional information regarding your services or products including costs, specialties, images, etc. You should add as much detailed information as you can because a more thoroughly detailed out listing within Google Maps will help make it easier for customers to see your dealership's listing show up on their search results.
You'll then be taken to a section where you can preview your listing and make any necessary edits.
Google will then require you to select how you would like to verify that you are a representative of the dealership.
You can choose to have a postcard sent with a verification PIN that must be then entered into an online authorization and verification form, or you can choose a phone call, where you enter the PIN during the automated call.
It will then take awhile for Google to set up your listing in the online map, but most dealerships have found that the listing is well worth the time and energy to get it done.
You can learn a lot more about Digital Marketing in the Automotive Industry by visiting the Automotive Digital Marketing Professional Community