I don't know if it's relevant but when I was using a FM transmitter before and it was connected to my ipod, the plug would stay live if the ipod was playing even long after the X was turned off (till song list ended). But if the ipod was off the transmitter/plug would shut down in about 15 minutes. I think that a live draw on a plug keeps the ibus from shutting down. Try turning on your dashcams accelerometer so it only runs while moving and shuts down after a few minutes of standstill... This might save you from a wiring job.

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"When the Team Chief said.... You're trapped in a hole with nothing but a goat and a slinky, what do you do? Stubby said, I'm not sure but it won't end well for the goat...." ~(Overheard) Last day, Phase 3, Q Course