It does that for a reason , it is very unsafe and most likely illegal . but my guess would be if it only works when handbrake is up then there must be a cable for that you could maybe disconnect.
Not only sensor for handbrake, there is also a speed sensor and it will not work when moving. Any mods that I have heard about have not been through software, only through wiring bypass. No really worth the hassle considering you can buy 7 inch portable dvd players for less than $50.
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