I have seen similar instructions selling on eBay for $4.99 on Buy-It-Now (here and here), but I question the legality of selling this information for any price. First of all, the modification is easy to figure out for any lay person with a nearby RadioShack. Second, it is illegal in most jurisdictions to bypass the video cut-off of an in-dash DVD player so that the driver can watch DVDs while driving, though experience tells me that there are some out there stupid enough to want to do just that.
Because I am an ethical darwinist, I will tell you how to perform this hack and I won't charge you a dime. If your IQ is such that you feel it is safe to drive while watching a movie, just make sure not to take anyone else out with you. But for passengers in the front seat, there is only one way to enable them to be entertained by watching their favorite movies on long road trips. Here is how to do it.
First, we need to buy the device. This can be found at Best Buy for $499. circuit City charges $599, but they will match any competitor price and I am loath to buy anything from Best Buy. Their customer service sucks. And Circuit City really needs the money. You can also find the system online for around a hundred dollars less, but who wants to wait for delivery, and how trustworthy are no-name generic online stores?
Next, we need to follow the instructions to get the stereo installed. I splurged and had circuit City install the device for me with one simple instruction. "Do not connect the green emergency brake cable. Just leave it coiled in the center console." As long as you do not modify the wire before leaving their shop, they incur no liability. They are not legally obligated to complete the install if the customer does not wish. besides, you could always buy the unit and do it yourself if they do not wish to fulfill this request. Save yourself the $100 installation fee.
We need to pick up a couple of items from our local RadioShack to complete the wiring job that the store failed to complete. First, you will need some form of a switch. A single interrupt switch is nice as you only need press the button once to enable the system, but a rocker works nearly as well. A rocker single-pole single-throw (SPST) switch will need to be turned off and then on to enable the device. Most interrupt switches available at your local store are tiny and will require some soldering. The larger SPST switches can be connected with crimp terminator leads that can be easily snapped on and off from the switch connectors. Lastly, we will need some sort of ring connector for the end of the lead. This only needs to be about an eighth of an inch diameter opening for my purposes, but you will need to see where you will be grounding to determine the best part to buy.
Take the long green lead that is supposed to connect to your emergency brake switch and connect the end to a ground. You can test potential grounding points before making the connection permanent by stripping the end of the wire and touching it to several potential targets while the DVD mode is turned on for the player. If the screen changes whenever you touch metal, this is a good place to ground. It would be helpful to leave the emergency brake off so that you do not accidentally ground to the brake switch which would be the normal install.
Once you have the end of the lead grounded, pull the wire to where you will mount the switch and cut it leaving enough wire to connect to each post on the switch. Excess wire is not a problem. It can be safely tucked under the console.
Strip each end of the wires at the location of the new cut. Attach a crimp terminator to each end and snap them on to the switch. If you want to be really creative, you can mount the switch inside your console. If you are not ready to mount it, use electrical tape on the connectors to keep them from shorting.
That is all there is to it. To test the circuit, turn on your car to the accessory position and insert a DVD. You should get a warning that DVDs will not play unless the emergency brake is applied. Toggle the switch off and then on (or simply push the button on a momentary switch and release) and the screen will change to a different warning and prompt you to press "OK". Pressing the OK button will cause the DVD to play and video to be displayed. Voila!