Well... the manual says:
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Parking Brake
Parking Brake Inhibit
When the pink "Parking" wire is connected to the vehicle
brake switch, the front TFT monitor will display video
only when the parking brake sequence is engaged.
Before starting the parking brake sequence, the radio
must be on with the video media disc inserted and
playing.
Parking Brake Sequence
There are two situations that can start the Parking Brake
Sequence (this is the preferred method). The timing
window is between 3 ~ 5 seconds.
• Parking brake is engaged (on) when the vehicle is
started or the accessory/ignition is turned on. To
activate video, the following sequence of events must
be completed:
a. Release parking brake for 3 ~ 5 seconds.
b. Reapply parking brake.
c. Video should be displayed on the TFT monitor
within 1 ~ 2 seconds.
• Parking break is disengaged (off) when the vehicle is
started or the accessory/ignition is turned on. To
activate video, the following sequence of events must
be completed:
a. Set parking brake for 3 ~ 5 seconds.
b. Release parking brake for 3 ~ 5 seconds.
c. Reapply parking brake.
d. Video should be displayed on the TFT monitor
within 1 ~ 2 seconds.
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If you want to connect it to your parking brake, then just find the wire that leaves the parking brake switch and tap into it.
If you want to bypass the parking brake switch and activate your HU any time you want, then you need to install a switch that connects that pink wire to ground when you toggle it. Look to Radio Shack or even Wal-Mart to get a small switch to wire in series with that circuit.
If you want to get creative, look for a timer circuit that is activated at startup... should be pretty easy to make it work.
Hope this helps.
Mark
p.s. If you bypass the parking brake circuit and then wreck your car watching DVD's, don't come crying to me.