I don't know anything about GPS or car video, but here's a few things you might want to have your "car guy" check out...
Check the audio out leads on the GPS system, if it has any.
Also, and this may actually be the problem. The GPS might only be a DVD reader, not a DVD player. If the GPS is one of those that has maps printed on the DVD, and can be replaced every few years (addresses change, new streets put in, etc.) it likely doesn't have audio (read) capabilities. Even if the GPS has audio "signals" like "Turn right at Grand Ave.", they're programmed into the DVD, they not being "read".
Ask the salesperson you bought the GPS from if it is supposed to have full DVD movie playback capability. If it does, I could only think of two problems: A) improper installation, or, B) you need some type of harness/adapter as a "in-between" your radio and the GPS system.
Like I said, I don't know anything about GPS or car video, so I maybe full of it. The above ideas are probably worth checking out, though.
Just got back from my "car guy". Here's the story...
I have a factory radio and factory DVD rear player. When he attempts to install a new radio (ANY radio), the audio goes out in the DVD. In my case, the radio is a Pioneer AVHP6500 (am/fm/cd/dvd). I'm also having the touch screen navigation put in, but he says that has nothing to do with this problem.
I know nothing about this stuff but he showed me the back of my factory radio. There are three places that wiring harnesses hook up to. The one in question is the middle one.
He showed me what was faxed from Pioneer - it was a schematic of what each wire did in that harness. He is able to "jump" the video portion but any attempts to get the audio back to the dvd are unsuccessful.
Does not make much sense to me! The Ford parts guy tells me that the two factory units (radio/dvd) will only work together and there is no wiring harness available to enable other manufacturers parts.
What is everyone who has a factory dvd going to do when they want to upgrade their radio? Based on what I'm being told, we're all SOL...
lol this is why I didnt replace my radio. I have a nice 2001 model pioneer radio that has an AUX input for things like a cd changer or dvd but heres what I discovered. The factory dvd doesnt not have RCA outputs there for there is no way to intergrade it to an aftermarket radio. I thaught about using a line output converter to it but that wont work because the signal from the dvd has next to no power. The radio has some sort of preamp for the dvd system. I love the way the dvd system looks on the roof liner and I dont want to replace it. I do have 3 sets of wireless headphones but sometimes my kids want to hear the Shrek Kareoke thru the system. You are correct in that we are SOL. There has to be some kind of preamp that will convert a low level wire input into a low level rca output. I haven't tried it yet but im wondering if just conectting an rca jack to the end of the stock dvd output will work. I guess I need to see if I can find out the output voltage of the dvd. I dont want to burn any thing up.
Yes it does. Kinda makes me wish Ford put a cheap ugly dvd in so I can change it....lol Hey quik thaught. Does your dvd player have two head phone jacks? Mine does so you can listen with regular head phones. I'm just wondering if something can be converted from that to go into the radio. O boy now I have to pull my radio out and start brainstorming again............ How much better did you say it gets?
I kinda have the same problem that you did a few years ago except I need to find a factory radio to work with my factory DVD in my 2003 Expedition. Do you have the part number (on the back sticker) for your original radio??