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I have a 37 year old car. The (classic looking) Bluetooth radio is by far the most complicated electronics on board.

When I switch off the car, for safety, anti-theft and leaking, the battery is disconnected entirely with a key.

The radio looses everything: paired devices, position of radio tuner, volume, BT/aux/radio mode etc. Whenever you start the car, you'll need to mash at least five buttons and knobs to either find a radio station or reconnect Bluetooth. Modern tech is often so smart it becomes dumb again.



You haven’t wired it properly. If there is no constant power wire just run one from the battery.


I have it wired like this deliberately.

As I pointed out, some pieces and parts keep using electricity. Amongst which is the radio. This will drain the battery. Slowly, but surely. If I don't use the car in 14 days, it (probably) won't start; but with this wiring it does, just fine.

Which is why I installed a [don't know the english word]¹, so that my battery is switched off entirely. Everything in the car is fine with that. Except for this "modern radio".

Hiding that switch in a somewhat unexpected place also delays theft. 37 y/o cars are easy to steal; this makes it slightly less so.

¹ here's an image: https://www.hsct.nl/wp-content/uploads/2014/10/IMG_8097-247x...


A car stereo is supposed to have two +12V input wires and one ground wire.

The yellow wire is named "constant" or "battery". The red wire is named "accessory" or "switched". The black wire is ground.

When the car is turned off, the red wire drops to 0V and the radio turns off. The yellow wire is supposed to remain at 12V to maintain memory state.

The yellow wire draws a very low amperage, and would take years to drain the battery.




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