I have a clarion nz409. Can I ground the park brake wire to get constant video play or do i need a switch?

the parking brake wire is a light green or dark green wire you need a toggle switch on and off connect to ground and the other to parking brake wire to simulate vehicle parking brake

This is a safety feature (and legal requirement) to prevent watching the video whilst driving

Find the wire for the parking brake... Get a (interrupter) toggle switch. Ground one side of the switch to a grounding point in the vehicle close to where you are gonna have it. Hook the wire for the dvd up to the other side of switch....When you want to watch dvd, flip toggle switch...

Install a toggle switch to the parking brake wire form the unit. One end of the wire goe to ground and the other to the parking brake wire. The unit needs to see the ground circuit switch; so,start the vehicle with the switch in the off position, then switch to the on( applying ground to the wire).

absolutely not......you run the parking brake wire to toggle switch positive and run the negative to a ground.

You can do like I did installing it in my 04 Civic Hybrid - find another wire that supplies a constant +5VDC and then it will believe the parking brake is always engaged and allow video. It's not legal to watch video while driving, but in my case, there was a wire bundle of around 30 or 40 wires harnessesd together that I wasn't about to jack with.

Also note that Clarion will not warranty any self installed NX or NZ 409 units. Something I hadn't realized when I got mine off e-bay.

connect the wire to a ground/negative point, please note this is a saftey feature.

If you have the old firmware then all you need to do is ground the parking brake wire..

if you have the new firmware(just bought the system) a toggle switch is involved:
1 - connect e-brake wire from dvd unit to the switch
2 - connect a ground wire from switch to the unit chassis(any good metal grounding surface will do)
3 - pop in a dvd, toggle the switch back and forth 2 or 3 times depending on what wire you placed where...and voilaa!! your dvd system should work in motion!!

I think the wire that should go to your hand brake is green, all you need to do to bypass this is hook it to an earth.

Clarify please-does the screen show "Audio Only" when a DVD is inserted? If so, this is because the parking brake lead is not set up to work. Normally, the green lead connects to the parking brake negative on the car. This means you don't get video unless the parking brake is set. To bypass this, you need to wire the green parking brake lead to one terminal on a toggle switch, then you run a wire from the radio ground lead to the other terminal. toggle the switch up and down and you should have video. You can get a pretty small toggle switch and mount it in a concealed place.
This is by no means advocating watching video while driving!!!!