Sorry... I have a JVC KW-V10 crew cab no onstar. I got the chime box, so I understand it's pretty much plug and play just looking for any helpful hints. And there is so many different "versions" of how to make the did play I figured I'd see if any one knew for sure.
To make the DVD player play while driving, there should be I believe is really light blue wire for the DVD power. The instructions tell you to tap/splice that into your parking brake power wire. Instead of the parking brake power wire, just find any regular hot 12V power wire and it will play as you drive.
As Blue said there will be a wire from your new JVC unit that goes to the parking brake. When you do as he recommended make sure to put a switch (toggle or whatever) that is somewhat accessible. I have mine in the glove box. I am not that familiar with JVC but Pioneer has a circuit that will figure out that you have overridden the feature (even with a relay setup). It becomes a pain sometimes but well worth it.
Second, again not sure about the JVC unit, but some Pioneer units have a depth issue with our dash. If this is the case, all you need to do is remove the metal tab. If you look in the hole the factory radio came out of there is a metal bar, the tab is tack welded on that bar. It is fairly easy to break the weld by hand or pliers.
As far as amps go… there are so many ways to hook them up and modify this that and the other, you would need to be very specific. How many amps and type, what are they going to be used for (front/rear/sub)? Simplistic single amp: run a 4 gauge wire from the positive terminal (put inline fuse within 12” of battery) through the fire wall (driver side behind brake mount system, big grommet, can’t miss it) to amp mount location in cab. I would run it down the driver’s side under the removable door plate and carpet, make sure it will not get pinched snagged or cut. Use the shortest ground possible to the amp, but make sure it is a good clean connection (wire brush or drimmel until shiny silver metal). I would also use 4 gauge if possible. Use a 16 or bigger gauge wire for the remote cut on from the head unit to amp. This can be run under the dash to the 4 gauge + power wire then run alongside power wire to amp. Run RCA cables from radio to amp, but try to keep them away from anything that carries voltage as best as possible. I would remove the driver’s seat or passenger (depending on amp location) and run along the drive shaft hump, same rule no pinch snag or area that would cut (you might have to also remove the back seat depending on amp location). Connect speakers as recommended by amp manufacture. Test and enjoy the sounds of your new setup. If headlights dim or you hear a high pitched whining sound do research on Big 3.