I had the same problem, try this 2006 Acura TL w/Navigation Carputer Worklog.
It allowed me to see when the power was off completely. You only need the power led. Also make sure to put 180ohm or 300ohms in line with the + side of the led for protection of burning it out (might not need it because the leds on board probably already has its own resistor I did mine as a precaution.
Also I recommend you fork out some $$ for the battery I liked it much better and set it to standby/hibernation after 5mins on battery or when the battery hits 95%.