Adding a 12v socket in Prius cargo by tapping leads going to my amp

Hello,

I have a 2005 Prius and want to add a 12v socket in the cargo area to charge my Zune.  

So I'm trying to find an IGN-ON only 12v source already existing in the back area, but no one at PriusChat has been able to help so far.  Using 12v always on is too risky b/c, other than when the engine is on, Prius gets 12v accessory power from a smaller than normal 12v battery (not from the batteries that power the electric engine).

I do have an amp installed in the cargo area.  It's been almost 4 years since I had the amp installed but if I remember correctly the '05 sound system did not have a 12v+ "on" (to tell the amp to power up) coming out of the sound system.  I think I had to buy some sort of accessory that listened in on one of the speaker lines to sense audio and when it did it sent a signal to the 12 "on" input on the amp.

So my questions are:

1.  Does anyone know of any 12v "ign only" on lines in the cargo area of the Prius, lines there when the car left the factory?

2.  Regarding the accessory I think I used to provide the amp with 12v-on signal, if I tapped in between that accessory's 12v "on" out and the amps 12v "on" input, to power my new 12v socket, would that cause engine noise or even work?  (I know that would mean my 12v socket would only be powered when the radio is on, which would not be ideal.)

3.  If 2 above won't work, is there another way to use the electricity being supplied my amp to somehow also provide ign-on-only power to my new 12v socket?

4.  Where would be the best place to connect the new 12v socket's ground wire if I'm doing any of the above?

5.  Would it be a good idea to put an inline fuse on the positive wire sending power to the new 12v socket?

Thanks.

Gary  

Hello,

It's the original poster with some new info / ideas.

Assuming my amp has a 12v + out (such as to power an electric antenna), could that be used to power the new 12v cigarette lighter socket?

I also have a Toyota OEM XM radio module back there that was added after I bought the car and am not sure if that might use whatever aforementioned accessory 12v+ out is available on the amp.

On the other hand, maybe the OEM XM radio module provides its own solution to my overall question of how to power an extra 12v cigarette lighter socket?

Thanks again.

Gary (CA--Prius)  

More info from original poster.

The amp is a Kenwood KAC-8542 and does not have any 12v out to power, say, an electric antenna.

I believe the accessory I've been referring to is made by PAC (Pacific Accessory Corporation), either the "Trunk-LOC" or something similar to it.   I'll be contacting PAC to see what they think of the idea.  

I'm also investigating an idea to get the best of both methods: connecting directly to the battery (to solve the problem of no IGN-only-on wire available and to get more charging time than just when I'm driving) but without the risk of running down the battery.  By using a battery operated programmable home thermostat to limit the time the Zune can draw power off the small 12v battery, even though it's plugged in all the time.  

More news from original poster.

I spoke with a tech support guy at PAC (Pacific Accessory Corporation) and he said that since all I want to plug into the 12v socket is the low amp demand Zune charge cable that I could tap into the 12v-on coming out of their Trunk-LOC product (a device that senses for voltage on a line (speaker wire) to then send a 12v-on signal to tell an external amp to turn on.)