mobile video in semi with air brakes

When installing an in-dash mobile video in a big rig equipped with air brakes, where can I find a "parking brake" connection for the safety lockout? I don't have a specific truck in mind; someone asked yesterday about the possibility of installing in a semi and I'm not certain how to do it, so I want to be prepared. Anyone installed in one of these before?

ok big rigs are all air brakes theres no wires for nothing on the air brake system except the abs. and with the way the law is these days i dont think it would be a good idea to put a hu like that. first of all its dangerous and second its  ilegal

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i know some stuff and what i dont know ill make it up feel free to ask

There should be a light somewhere that turns on when the air brake is engaged. Use that and a relay to convert the polarity if needed.

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sorry to be so negative but the semi trucks tha have air brakes have two kinds of air aplications service brake that engages when you press on the brake pedal and you get your brake lights and theres the emergency or prking brake that when engaged you get no lights at all not even on the dash what you can do if you wana do this is put a brake pedal switch wich you can get at any truck parts store and put it to the emergency (parking) brake air line you would have to play around with it for a while but you can get it to work all the switch does is it works with air pressure so you can just tap into one of those air lines.

let me know if you do this and what truck your using it on

also i just thought ill let you hnow in slot of the big rigs you have to find wire by wire (+12, ground, speakers) because all the wires in the whole truck are the same color.

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i know some stuff and what i dont know ill make it up feel free to ask