I had an opportunity to put the volt meter on the GY/YL wire today as suggested. Hooked up the battery, ran a ground wire from the battery terminal to the volt meter ground and bared the GY/YL for a good contact with the positive volt meter lead. With the key in the off position, no voltage. Now with the key in the run position to light up the reverse lights, I checked the GY/YL wire and voila 11.88 volts. So with the key in the run position I now put the car in neutral and check the GY/YL wire and still 11.88 volts. Tried all the other shifter positions and still 11.88 volts. So not what I was expecting. What this suggests to me is that if I connected the back-up signal lead to this wire I'd have voltage going to the nav radio whenever the key is in the run position. Is this what I want? Have I performed the test correctly?