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Anyway, yes, it would require a diode. The switch will control a ground. The diode will go between the output of the switch and the actual parking brake output. The wire to the HU needs to be tapped above the diode. Make sure the mark is closest to the output to HU wire so the signal gets through.

Pretty easy to do, but even easier to do like Selbyl suggested and wire it to a ground. Only problem that may pop up is if that unit has navigation built in and you intend to use it. If it sees vehicle movement with the parking brake on, it knows something is fishy and will probably give you an on screen message that will annoy the crap out of you. Easy way around this is to just wire in a switch to that input wire. Flip it off when you know you wont be using video, flip it when you want video.