# Where to find 12V positve while cranking



## fabric8 (Jul 4, 2000)

Can anyone tell me where I can find a switched 12V source that remains active *while* cranking?

I've tested various wires in the ignition switch - the starter wires gives +12V only when the starter is engaged but has no voltage in the ACC or OFF position; the ACC wire gives +12V when the key is in the ACC position, but when you turn it to crank the starter, it has no voltage.

I also tried the 75x terminal as well, but it also cuts out when cracking/starting the car.

I need to find a +12V source that turns on with the ignition (with either the key in ACC or ON) and stays on even while cranking the engine.


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## TaTaTaTUrbooooo (May 25, 2013)

fabric8 said:


> Can anyone tell me where I can find a switched 12V source that remains active *while* cranking?
> 
> I've tested various wires in the ignition switch - the starter wires gives +12V only when the starter is engaged but has no voltage in the ACC or OFF position; the ACC wire gives +12V when the key is in the ACC position, but when you turn it to crank the starter, it has no voltage.
> 
> ...


run direct fused switch to load neutral ground without a switch goodbye battery


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## fabric8 (Jul 4, 2000)

TaTaTaTUrbooooo said:


> run direct fused switch to load neutral ground without a switch goodbye battery


can't make sense of your response. I just need a source for a +12v switched (via ignition) wire that stays on while cranking.

I'm trying to connect a Bluetooth stereo receiver (which I've done on a number of other cars). Normally, I connect it to a lead from the radio that gives +12V power when the radio comes on, and cuts off when the radio turns off. But the key sense on the Audi is messing me up. I tried connecting to the acc wire that comes off the radio which normally goes to the CD changer (but instead I have it going to a Dension iPod interface and have tapped it for my Bluetooth receiver). But with Audi's key sense, when the ignition is turned on, it gives power to this lead and turns on my Bluetooth device even though the radio is still off. But when I start the car, cranking kills this +12V line, then it comes back on once the car has started.

The problem I'm having is the Bluetooth receiver doesn't like this sudden loss and restore of power. Once it powers on, it needs to stay on and not have any power interruption while the car is cranking.

I may just end up using an SPDT relay to achieve this unless someone can give me an answer.


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## TaTaTaTUrbooooo (May 25, 2013)

i was saying just run a wire direct off the battery with and inline fuse that can switch the load on and off . or install an inline shunt to take the brunt of the surge. or wire in a capacitor . either way without a switch your battery with drain


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## motorlager (Sep 26, 2005)

The easiest is to get a fuse tap from your local autoparts store and run it off of fuse 31 or 32.

If you look at your fuse box there is a bridge running down through fuses 6, 7, 31, and 32.

Its a "15" power which is on when the key is on and does not cut out during cranking.

Make sure you tap into the bridged side.


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## fabric8 (Jul 4, 2000)

Thanks for the replies, guys. I didn't see these followup replies until I already tapped into fuse #10 (S contact) which I had previously tapped into for my V1 radar. So now my radar and 12V 1A USB power adapter (to power my bluetooth receiver) are tapped to fuse #10.

The weird thing is that my radar "reboots" while cranking, yet the 12V 1A USB power adapter doesn't, so my bluetooth receiver stays connected to my phone. I suspect that the V1 is super sensitive to power fluctuations and maybe my battery is going bad, so while cranking, voltage drops below 12V and my radar dies.

However, the USB bluetooth adapter which is plugged into the 12V 1A USB adapter is really only getting 5V 1A, so even though power drops below 12V while cranking, the USB power adapter can still deliver the 5V 1A that the bluetooth module needs.

BTW, if you guys are interested, this is what I did. I bought a Aux-in adapter for my OEM headunit (dension or Dice work just fine). I then bought this bluetooth stereo receiver for $7.50. It connects to the aux-in on the aux-in adapter with a 1/8" stereo cable.

It needs power, so I just bought a 12V usb adapter to power it. I took it apart and soldered wires directly to the + and - on the circuit board and ran those wires plus an inline fuse to fuse #10 and ground. I connected a microusb cable to the other port of the USB adapter to charge my S3 phone. No wires visible (other than the wire to charge my phone), and the bluetooth sound is perfect quality, and my cigaretter outlet is free.

And it works great. I've done this on my Passat, Honda Pilot, A4 and now my TT. Best thing about it is that I can stream sound from any bluetooth compatible device whether its an iphone, ipod, android device, or ipad.


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## speed51133! (Aug 5, 2002)

the starter is such a drain on the battery that all the current rushes towards it.

try running a power wire direct to the battery + and then a GOOD ground, preferable the battery -.

If that doesn't work, time to let go.


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