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Thread: head unit problem...

  1. #1
    Low Bitrate sounder's Avatar
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    head unit problem...

    I have a Sony MEX-1 head unit and did the installation myself. All is well except one thing, Every time I turn on the car I have to reprogram the clock settings and all my audio tweaking. It doesn't retain a memory, even though it has one. Now my first thought was oh, my acc line is not hot or something...or maybe I didn't wire it right, but after inspection I was looking at it, and all my wires are right. Except for one wire which is the acc line in. Now I used the cigarette litter as the supply for this voltage, but I'm thinking that the cigarette liter doesn't work when car is, which would explain the problem, but any ideas as to a constant output while car is off would be great, maybe lights?? I don't want to fudge anything.

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    Low Bitrate stkdidy ntshidy's Avatar
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    the yellow wire in the harness connects to 12v power from the ignition...the red wire connects to constant 5volt power...unless you have the red wire hooked up properly, it disconnects the deck from electricity every time you turn off the car, and will reset all settings...
    2005 Mustang GT:
    12w7...arc audio kar1000.2t...jl 300/4 pushng focal 165k2p...pioneer premier deh-880prs...tm-701l...audiocontrol eqs
    want: my stereo actually IN the car

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    Quote Originally Posted by stkdidy ntshidy
    the yellow wire in the harness connects to 12v power from the ignition...the red wire connects to constant 5volt power...unless you have the red wire hooked up properly, it disconnects the deck from electricity every time you turn off the car, and will reset all settings...

    you know what, I dont believe I have a 5v line in my 78 camaro, I think its all 12v...its also 1 in the morning for me, so I aint thinking straight, but having 12v into a 5v line would not be good. It also has another freaking prblem....I cant get the cd tray to close, unless I am driving. I cant park and change cds. Also it dosnt matter about alt output, cause I can rev that bitcch upto like 5k rpm, and still wont take the cd, but I garentee you when I start rolling down the driveway it takes the cd. I think it has to do with the hdd. I dunno.
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    Low Bitrate sounder's Avatar
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    would giving the acc line a straight shot at the battery fix the prob?
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    Low Bitrate stkdidy ntshidy's Avatar
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    is there any way to run a wire from the battery to a 12-5v filter or sumn, and run that to the red wire? i didn't realize how old the car was, so i don't personally have any experience wiring a deck in that situation. all i can say is search the web for wiring diagrams for both your car and for the deck...?
    2005 Mustang GT:
    12w7...arc audio kar1000.2t...jl 300/4 pushng focal 165k2p...pioneer premier deh-880prs...tm-701l...audiocontrol eqs
    want: my stereo actually IN the car

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    Variable Bitrate MeanGT's Avatar
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    Quote Originally Posted by sounder
    you know what, I dont believe I have a 5v line in my 78 camaro, I think its all 12v...its also 1 in the morning for me, so I aint thinking straight, but having 12v into a 5v line would not be good. It also has another freaking prblem....I cant get the cd tray to close, unless I am driving. I cant park and change cds. Also it dosnt matter about alt output, cause I can rev that bitcch upto like 5k rpm, and still wont take the cd, but I garentee you when I start rolling down the driveway it takes the cd. I think it has to do with the hdd. I dunno.
    NO car has a 5v Line, be careful. If in doubt, buy a voltmeter and measure it and see. In order to supply 5v you would have to tap into a computer power supply, or another power supply. Also, NO head unit is going to call for 5v in.

    90% of all head units are wire like this:

    Yellow Wire: CONSTANT +12v (Ie: run it straight to the + on the battery)
    Red Wire : SWITCHED +12v (Ie: Run it to a fuse that only gets voltage when the key is turned forward)
    Black Wire : CHASSIS GROUND (ie: run it directly to a bolt that is connected to part of the frame, or chassis, dash bracing, or anything solid metal)

    It sounds to me like you have the yellow and red wires reversed.
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  7. #7
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    From the original post I don't think this is a computer, it is a standard Head unit.

    there are two power wires, one which connects to the ACC of the ignition and get +12V when the car is on (not necessary for engine to be running) and another which goes to a constant +12V supply (direct to battery).

    You can connect both directly to the battery (or a constant 12V) but the Head Unit would be on when you switch the car off and could drain the battery. You would have to hit the power off button (if it has one) every time you got out the car.

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    Low Bitrate sounder's Avatar
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    yeah it has a power off button and I wouldn't mind using it, if that meant that I could retain the clock and audio settings. I don't have the wires crossed, I used a 12 plug gm harness, and the only wires that go to that are the 12v const. illumination-orange,antenna, and gnd. So those are simple. The one that are not in the wire harness are the speaker wires, which are custom laid, and that freakin red 12v wire. That red one is not 5v, I checked it, the wire calls for 12v. So its down to what 12v i give it. now I originally gave it the one from the liter plug, but I think that that cuts completely off when car is off. I think that red wire calls for a constant all the time power, cause how else is it going to retain memory with out some trickle. I have been trying to contact Sony, but you know how that goes.

    ~Sounder~
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  9. #9
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    read your own post, and that of MeanGT , in your post you say in the harness is a 12V Const, that should be the one connected to a permanent supply (ie battery)

    the red one 12V goes to ACC or the permanent if you want it to.

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    well, there is a stero harness in the car, that has 4 wires in it, they are from the original stero. Now I bought a aftermarket harness ti connect to the gm one. There is no doubt in my mind that yellow goes with yello. So I wire that into the harness. The red wire is the only one not in the harness but connected to an acc line. My problem is that it does not retain any memory when car is cut off for more than 30 sec. So I was thinking that there must be a wire that needs juice all the time. I think its the red wire, but my acc line is not active when car is off...like I cant turn on the wipers or light a cig, or play the radio when the car is off. That means there is no power on the red acc line when ign is not active. So I think I have to run a wire straight from the battery.
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