This article describes how to reassign a vehicle's primary group. The vehicle should have initially been assigned to a primary group when it was first assigned to groups (see Assigning a Vehicle to a Group for details), but you can also follow the steps here to assign a primary group if this hasn't been done at all yet:

Note: The vehicle must be assigned to a primary group; if it isn't, it won't appear in Fleet Tracking or any of the reports.

First, make sure that the vehicle is assigned to the group, as shown in Assigning a Vehicle to a Group.

1. Click >> Vehicles.
      
2. In the Vehicles list, click  to the left of the vehicle's number. 
    
   
3. On the Edit Vehicle screen, click the Groups tab.
    
   
4. Click the far-left check box in the row of the group you want to make the vehicle's primary group.
           
5. Click Make Primary.
    
   The check box under Primary to the left of the group name will become selected, and "Primary" will appear after it in parentheses.
    
6. Click  at the top right of the screen.