HiFiSi - thanks for the time you spent to respond. The only real way to tell what is going on will be to get into the pinout and hook up my scope. If the video signal is back-fed, I'll just leave it out of the Pioneer input and only go to the RCA. Noise from the ground is my largest concern.
So, maybe a $100 total investment. I have like 6 of the A/V cables laying around my house, so no biggie there. Maybe if I fry the radio then it will be $1K for a new HU and iPhone. IMHO, it would be worth it, and I'll take that risk. Heck, now it is a personal challenge.
Because, as you all