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BMW E46 Android head unit

A little context:

I have a head unit, that I want to have constant power through ACC. Basically, it's an android tablet customized for my car, but the manufacturer (unbranded Chinese) did not take into account that android tablets are actually never supposed to be fully powered down. Therefore, I'm well down the road before the unit is ready to go.

The question:

How can I wire the ACC to always have power? Is it as simple as jumping the yellow and red wires like I do when I run my unit off of a PC power supply? I just want to make sure that is safe for the car, I know that might sound a bit stupid. Car wiring is foreign to me and I want to make sure I know all of the dangers before I fry a very expensive competent in my very expensive to maintain German vehicle.

What I think I already know:

I understand that by constantly leaving the radio powered it will drain the battery, Having done some tests on the bench; I think this will be negligible as I am able to put the device into a hibernate state. If draining the battery is the big risk then I'm not too concerned about that.

  • 1
    I'm not sure in your application, but would bet if you just jumped your two wires, you'd be providing power to all of everything hung off of the ACC. I think I'd just plumb a hot lead off of your fuse box and run hot to your head unit directly and not mix the ACC into this ... but I'm not a car electrician either :D – Pᴀᴜʟsᴛᴇʀ2 May 19 '14 at 0:07
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    @Pᴀᴜʟsᴛᴇʀ2 That's a reasonable and functional answer. I'm not a car electrician either, but I'd give it about a 100% chance that: Yes, ACC mode powers all the accessories (it's equivalent to leaving the ignition in ACC) and, yes, wiring a (fused, for safety) hot lead from anywhere prior to the ACC relay / ignition switch / wherever it's switched would be just fine. Check E46 wiring dgrms. The only thing to watch out for is the tablet draining the car battery over time, so maybe keep a nice compact jump starter handy for emergencies. If you don't convert your comment to an answer, I will, heh. – Jason C Aug 11 '16 at 14:54
  • @JasonC -Dun ... :o) – Pᴀᴜʟsᴛᴇʀ2 Aug 11 '16 at 20:37
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What you want is probably not what you'd like, see Paulster2's comment. What you are looking for might already exist.

On most modern vehicles, the head unit has an "always on" power lead and a switched power lead. The always-on power allows the head unit to retain memory and do graceful shutdowns or disconnects on optical disks, USB and Bluetooth.

If this power lead does not exist on your model vehicle, create one by running a lead from the battery to the dash. Place a fuse in the lead near the battery junction, so the majority of the run is fused.

inline fuse

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    Liking your answers today. Great job on converting this from unanswered to answered. Cheers! – DucatiKiller Aug 11 '16 at 16:49
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I'm not sure in your application, but would bet if you just jumped your two wires, you'd be providing power to all of everything hung off of the ACC. I think I'd just plumb a hot lead off of your fuse box and run hot to your head unit directly and not mix the ACC into this.

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