1. Attach a weight on a pot pulling it down to ground. When the car moves and is moving it will change the pot reading in small steps by moving it back and forth. When the car is not moving for sometime, say 30secs or 60 secs. etc, then you will read a constant pot value AND know that the car is stopped.

OR
2. Short the wiper so that driver will always know that the GPS is running.

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