Install of Backup Camera: Need Troubleshooting Help... won't turn on!

Ok... I've been puzzling over this most of this past weekend and can't figure it out.

I'm installing a backup camera in my 2000 Tacoma and my headunit isn't detecting the camera. I've narrowed it down to the power/ ground I'm running from the driver's side tail-lights.

I'm connecting the power side of the cable to the power side of the center-light (the reverse light) in the tail-light assembly. The ground of the cable is connected to the ground side ... the side that is connected to the "outside" of where the lightbulb case is.

I've checked continuity of the lines (one end is wire the other end goes in to what looks like a 5mm audio jack). When the power to the tail-light is off (ie, the truck isn't in reverse), I show good connectivity from the tail-light power side to the "inside" of the jack-end of the power cable. I also show good continuity to the outside/ground of the audio-jack-end and the ground side of the bulb case inside the tail-light assembly.

Now here's the screwy bit. When I go in reverse (power to the reverse tail-light), I can see ~10V on the tail-light end of the wire to ground inside the tail-light. But, when I check the audio-jack-end, I show ~0V. Ground to Ground still shows good ... but when I check the power side (inside the tail-light) to the ground side of the audio-jack-end ... my multi-meter enters protect-mode.

So, uh, what's going on? How do I fix this?

Thanks