The radio should be fine with the 10A fuse. I would start by trying a different fuse to tap into and see if that fixes it.
Tried to tap into AIRBAG (IGN) and the same thing happened. It wasn't necessarily when the stereo turned on, but when it tried to play a CD that everything went kaput. I forgot to turn the car off when I pulled the tap out of the ignition, and when I pulled it out you could instantly see everything shoot to life. So I have no idea what's going on. Totally lost. Not good at this kind of electrical stuff at all.
For the sound, you only use the RCAs if you have an amp attached to the radio. Otherwise the sound needs to go out the regular wires (your green, white, grey and purple). When checking the voltage, you are not looking for any specific value as that is volume dependant. You just want to know that it is there.
It would appear that there is something coming out of the speakers. I just uncovered the green wires and tested them, and it shot anywhere from 0 to 1.8A, averaging around 0.3A. This was before the harness connection, though. I'm not sure how I would test whether or not there is any signal getting past the harness without stripping wires.
I would advise not hardwiring to the car harness. Not only will it be worse than this experience, but it could cause even more problems.
That is exactly what I didn't want to hear. If the harness is a POS, which it appears it is, I don't know what I'm gonna do. Literally the only harness I could find that came out and said "yes, it will work with your make/model" was on eBay. I couldn't find any from any reputable dealers (like Crutchfield), so I went to eBay. I found
this one from Crutchfield, but when I put my car into the car selector thing it tells me it doesn't fit. There's
this one but, again, it says it's for a 2006 G7, whereas I have the 2007. I found
this thread on the site of a guy going directly into the wires with, what it seems, some success. Then again, that doesn't solve the problem of the power tripping or whatever is happening.
This whole mess of an ordeal is getting me super frustrated. And the only solutions ever seem to be "throw more money at it and buy X and Y."
It's to the point now where I'm considering just driving the car and the deck to a car audio place and leaving it there and telling them to do it. I'd rather pay out all at once then keep trying to piece away at it, spending the same amount of money anyway. Do places like Carphonix even do that? Let you show up with your own stereo?