I was working on configuring my RaceCapture Pro in-vehicle today and had it hooked up to my computer while it was concurrently powered by the vehicle, so I could easily download configuration changes. When I turned off the ignition key I was surprised to see some idiot lights still illuminated on the dash. Measured voltage across the 12V +/- pins of the RaceCapture Pro and saw 3.3V. Promptly disconnected the USB cable from the computer and the voltage dropped to zero and the idiot lights went out.
It's probably not a good thing to be trying to power up the vehicle through the computer's USB port when the ignition is off. Maybe a diode on the 12V power to the RaceCapture Pro could prevent backfeeding to the vehicle in such case?
Hardware board improvement suggestion
Moderators: JeffC, rdoherty, stieg, brentp