Originally Posted by bluecoupe
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?
Two possibilities;
Wrong wire
Bad Test.
Confirm the polarity of your test probes.
I would not bother running a ground to the battery. Any metal surface on the body will give ground. I like the top stud that the cover to the factory amp bolts onto.
Tests would be as you described
Positive probe on wire
Negative probe on ground
make sure meter is set for DC volts NOT Ohms reading...
Car Off
No Volts
Key On engine not running (neutral with brake on)
no volts
Key On engine not running (reverse with brake on)
>11 volts
If you still get the same test results you got before (power no matter position of transmission) clean up that wire and tape it off. Instead use the lead behind the side panel in the back of the car that goes directly to the reverse lamp in the diagram I showed previously.
You should be able to easily test it the same way and get the expected results cited above. You can easily see the reverse lamp lit or dark and only have power when it's lit.
As I said, I decided against using the wire in the floor up front because I didn't want to unbundle the harness and I had an easy short run from the reverse lamp to my control box. For you it would just be a single 18g lead from the reverse lamp lead under the carpet and side trim (probably can sneak it in there without removing anything) all the way up to your unit.