So I have a 2004 toyota tundra SR5 4x4 4.7L. It had the stock head unit in it which consisted of a CD player and cassette deck in a single, double din head unit. Since I'm not really a big car audio enthusiast and this is my work truck, I never changed it out. I decided to buy one of those Chinese "Konifo" double din head units from amazon https://www.amazon.com/dp/B08V1HJKB8/?tag=caraudiocom-20 . When I hook it directly to a 12v battery, it powers up right away, so I know it works. I have the service manual for this model truck so I have the wiring diagrams. In the stereo wiring from the truck there is only one ACC wire and one constant 12V wire. Radio ground wire is the brown wire. Hooking the volt meter to the constant 12v wire reads 11.6v with the engine off and 12.65v when running. The ACC wire reads 0 volts with key in off position , 11.6v with key in ACC position and 12.65v when running (with the black lead of the volt meter on the brown ground wire) Connect the head unit and the voltage disappears completely from the ACC wire and drops to 1.9volts on the constant voltage wire. Is it possible the truck's computer senses something other than the factory head unit and kills the voltage to these wires? I have never read about another 04 Tundra doing this. I checked this again and again, unplug the harness from the head unit, insert probes into the harness, back up to normal voltage, plug the unit unit back in, voltage disappears, unplug and connect directly to 12v battery and it powers right up again. Has anyone experienced this? I think if I ask anyone , they wont believe its really doing this, it doesn't even seem scientifically possible.