Sony car radio

[montstpere]

why does my mex bt3900u not switch off with my ignition

[Drumzman · Accepted solution]

Hi montstpere,

This depends on two things: your car, and the way you have the BT3900U wired up.

The BT3900U has two power wires a red, and a yellow colour coded wire.  The yellow wire must be connected to a permanent 12 volt feed in the car (that is where 12 volts is supplied even when the car is switched off with the key out of the ignition).  The red wire is designed to be connected to a 'switched' 12 volt supply i.e. one that is only live when the car's ignition is on (or is in the 'accessory' position, which not all cars have).  However, it is possible to also connect this red wire to the same permanent feed as the yellow lead - if you do this then everything will work fine, but you can only turn the unit on and off using its own power button - this is the situation you have and means you have to remember to turn the unit off each time you leave the car.

I've included a picture of the options you have to connect your BT3900U to your car, but not all cars have a suitable 'switched' feed so it is possible you might not be able to get the unit to turn on and off with your car's ignition.  Also, you will see from the picture that there's a provision to reverse the position of the red and yellow wires as some cars supply the permanent and switched feeds the reverse way round to others, so this is always worth trying (you can't do any harm trying this, it just won't work!).

Situation 'a' is where your car has a separate permanent and switched feed which will make the unit turn on and off with your car's ignition.  Situation 'b' is the same, but allows the red and yellow wires to be reversed for some cars as I mentioned.  Situation 'c' effectively what you have at the moment.

Hope this helps anyway.