This page also seems to indicate that the fatter wire (the constant-on
wire) is the main source of power for the radio, and the skinnier wire
(switched) is only used to wake the radio up.

<http://avic411.com/index.php?/topic/36319-which-wire-is-the-power-source-yellow-or-red/>

"Without a doubt B+ (the yellow wire) is the main current carrying wire,
but this is only up to a point, as you have seen due to the radio fuse
not being more than about 10A typically on vehicles. Acc/ignition is
just a turn-on signal. While it can be used at a lower current
application, it is not typically meant for higher loads."

--
Jack "Rocket j Squirrel" Elliott
1984 Westfalia, auto trans,
Bend, Ore.

On 09/01/2015 07:57 AM, Jon VO wrote:
> Well, my understanding is a bit different; the ignition switch controls
> /switched/ power to the stereo, and is the source of the amplifier &
> control power which is usually multiple amps for a high-powered stereo.
> The other continuous power lead is supposed to draw only a few milliamps
> to keep the memory charged and for control functions, and is powered all
> the time. At least that is the way the stereos worked when the Vanagon
> was current. If you want to reduce the current through the ignition
> switch, you would need to add a relay, and I believe some newer vehicles
> already do this.
> Jon
>
> On 9/1/2015 8:45 AM, Rocket J Squirrel wrote:
>> The keying wire itself draws little current, it just provides a signal
>> voltage to the unit to put it to sleep or wake it up. The designers
>> assume that you don't want to draw a bunch of amperes through your
>> ignition circuit, so it's the the always-on wire that is the main source
>> of power for the unit.
>>
>> How much current the unit itself draws from its always-on wire when
>> asleep (standby) is a matter of design. But the key wire is not a
>> significant current-drawer.
>>
>> What I'm saying is that you can put the unit into standby with the key
>> wire and it can still be drawing hundreds of milliamperes through its
>> always-on wire. That's the one you have to watch out for.
>>
>> --
>> Jack "Rocket j Squirrel" Elliott
>> 1984 Westfalia, auto trans,
>> Bend, Ore.
>>
>> On 09/01/2015 07:30 AM, Jim Felder wrote:
>>> I remember when you went through all that, about the same time I bought
>>> my radio. So, using the keyed hot wire will draw very little or no
>>> current? I like the idea from a previous post that I could install a
>>> switch to connect it to either circuit, aways hot and switched hot.
>>>
>>> Jim
>>>
>>> On Tue, Sep 1, 2015 at 9:26 AM Rocket J Squirrel
>>> <camping.elliott@gmail.com <mailto:camping.elliott@gmail.com>> wrote:
>>>
>>>     Many car stereos/radios don't really turn off. They mute and the
>>> front
>>>     panel goes dark, the power amp sections shut down, and the
>>> controls go
>>>     to sleep, but they are still partially on and drawing current. I
>>> guess
>>>     the manufacturers assume that you drive your car frequently.
>>>
>>>     The current draw is through the main power wire, the other wire,
>>>     frequently connected to the ignition switch, doesn't draw much
>>> current
>>>     at all -- it is used to signal the unit to wake up.
>>>
>>>     I had to search high and low to find a unit that actually powers
>>> off --
>>>     not only from the front panel power button, but from the remote,
>>> too. So
>>>     I could turn off the music when I get into bed rather than have
>>> to lean
>>>     up to the dash to shut things down.
>>>
>>>     --
>>>     Jack "Rocket j Squirrel" Elliott
>>>     1984 Westfalia, auto trans,
>>>     Bend, Ore.
>>>
>>>     On 09/01/2015 06:08 AM, Jim Felder wrote:
>>>      > About a month ago I wrote about having installed two pairs of USB
>>>     ports and
>>>      > an LED voltage display in my Vanagon. The round double outlet on
>>>     the dash
>>>      > took the place of my factory Eberspacher heater knob and the
>>>      > outlet-and-voltmeter combination set neatly into what was the
>>>     rear ashtray.
>>>      >
>>>      > That's when I noticed a drop in voltage that would flatten the
>>>     battery
>>>      > after a couple of days of being parked. Long story made very
>>> short, I
>>>      > discovered that it was my radio in standby mode that was
>>> draining the
>>>      > battery. I pulled the fuse to the radio on Saturday and this
>>>     morning the
>>>      > voltage is showing 12.9, exactly where it was when I pulled
>>> the fuse.
>>>      >
>>>      > The reason that this was unknown to me all this time is that
>>>     coincident
>>>      > with the addition of the USB ports the Vanagon was, except for
>>>     use of my
>>>      > wife's Prius, my daily driver had been the Vanagon. When I got a
>>>     TDI Jetta
>>>      > the Vanagon started sitting for days or a week at a time, and
>>>     that's when
>>>      > the problem showed up.
>>>      >
>>>      > I could wire the radio to the switched 12v circuit that no doubt
>>>     came with
>>>      > it, but then I would have to have the key on to listen to
>>> music while
>>>      > camping. Is anyone using a switch on the circuit, and if so how
>>>     was it done
>>>      > and how does it work out for you?
>>>      >
>>>      > Jim
>>>      >
>>>
>