I don't use the location triggers because GPS doesn't work very well inside buildings (at least here at work where I'm on floor 4 of 5), but I'll walk you through how I have my car mode set up.
1) Create a profile for your car
- On the profiles screen, click Menu -> New Profile and give it a name
- The star on the left of each option, when selected, means it will update that setting. If it's not selected, it won't affect that setting. So if you don't want your ringtone volume to change, make sure the star next to ringer volume is grey.
- Since you want BT to turn on, make sure the star next to it is red (or yellow or whatever color your theme changes it to) and then make sure the checkbox to the right is selected.
- You might want a couple other things -- I have it automatically turn the screen timeout to Never, Silent mode OFF, Ringer volume max, Media volume max, In call volume max, Speaker phone on, brightness to auto and GPS on
2) Now, you need to set up a rule to actually trigger the profile
- Click BACK to get to the Setting Profiles main menu
- Click on the RULES tab
- Menu -> New rule
- Menu -> Add condition
- Scroll down and select Docking State
- Select in the car dock
- Menu -> Add action
- Select Activate Profile
- Choose the profile you created in step one
Now go test it out.