Is there a way to enable Hotspot when connected to a specific Bluetooth source?

You can use Tasker to accomplish this

Profile (or Trigger)

Create a Profile which allows triggering of the Tasker upon bluetooth connection:

• Go to Profiles Tab and click the "+"



• State âž¡ Net âž¡ BT Connected [Name : Name of your car BT, Address: MAC of your Car BT)




• Tap back to exit from this window

Task

You will notice as soon exit, you will be prompted to link this to a Task

• Scroll all the way up the Task list select "New Task + "



• You can name this Task AutoTethering or anything or leave optionally as anonymous task.




• Click "+" to add new Action




• Net âž¡ WiFi Tether (Set On)

Explanation: When Tasker detects the device is connected to another device(car) via bluetooth, it will run a task that activates wi-fi tether.

This should work cheers.