GPS Logger Trigger Circuit Integration
You can achieve this by simply using an optocoupler such as EL817 which will completely isolate your control circuit from the high voltage side.
You can connect an optocoupler to your existing system as shown below. And don't forget to turn on an internal pullup resistor of the Arduino digital pin which you are going to use as Input.

You can also do the same thing with no optical isolation with an NPN transistor such as BC547.