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Thread: Car headunit wiring query.. Calling all electrical guru's!

  1. #1
    Senior Member Thirteen13's Avatar
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    Car headunit wiring query.. Calling all electrical guru's!

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hey Guys,

    Sorry in advance if this is the wrong section, i was unsure which was correct one ? Plus im bit noob at this stuff!

    Ive just purchased a Pioneer AVH-P4450. So basically Double din touchscreen DVD headunit which is 2012 model.

    I've wired it all up using one of those lovely $15 repco harness so keeps the car harness all clean and tidy.
    Currently its the deck running off the stock wiring and stock speakers and in 2000 celica it sounds quite good.

    Down the track however im going to be switching to a proper amp and 4 aftermarket speakers. So with this in mind, I currently dont have the "handbrake" wire connected as i want to bypass it. I understand you need 4 pin relay and you basically ground out the relay, supply the "green" handbrake wire to one side of the relay and use the blue/white amp power wire to supply the power.

    However my query comes from that fact that at the moment the power source will feed the relay only. But down the track when i want to wire in an amp, I want to know the wiring setup and if it will still work fine. Ive read that the Amp wire runs very low power and its purpose is to signal to the amp to switch on. However drawing some of that power to the relay, will this cause any issues or problems. Is there anything i should be looking out for or something else i should do ?



    Here is a basic diagram of the image, the point im interested in is in the red circle. Basically Blue/White wire going to the amp and being split either part way/at the harness connection/wherever to feed the relay.

    Also with the 2012 model of pioneer decks does this method still work for bypassing handbrake ?

    Cheers guys, thanks for your time and help

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    Not entirely sure what you mean by "handbreak" wire, I assume it's for the switch that detects the handbrake state and mutes the video when your handbrake is not on? Just in case you weren't aware, bypassing this feature and displaying full motion video on the display is technically illegal (at least here in VIC), you can be booked for it.

    I gather you're trying to use the relay to pull the handbrake wire to ground to emulate the handbrake switch being "activated"? I don't have any experience with this style of headunit, but from a general electrics standpoint, why do you need a relay? I'd just tie it to ground.

    But to answer your question, the remote line will *probably* drive a relay and provide enough signal to power the amp up, if not there are some other options.

  3. #3
    Senior Member Thirteen13's Avatar
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    Yeah it is illegal i think everywhere in AU, but im not using it to watch a movie while i drive I had a laugh. There are other functions which are locked out.

    Im unsure also why the relay and what not like i said im a noob, but yeah ill try earth it out see wat happens.

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    Mate you dont need a relay for any of that. Earth out your handbrake wire in the harness and you wont have an issue with the video as previously stated, but as also stated by yourself aswell, it is illegal. As for the remote wire (amp wire), just run it straight to the amp... No need for relays or anything weird like that. Car audio is a piece of cake mate, just dont try and make it complicated

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    Senior Member Thirteen13's Avatar
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    Quote Originally Posted by ausfitter View Post
    Mate you dont need a relay for any of that. Earth out your handbrake wire in the harness and you wont have an issue with the video as previously stated, but as also stated by yourself aswell, it is illegal. As for the remote wire (amp wire), just run it straight to the amp... No need for relays or anything weird like that. Car audio is a piece of cake mate, just dont try and make it complicated
    There are a few features on the deck like using the keypad to make bluetooth calling which gets locked out when the handbrakes isnt on, hence why i want ot bypass that, cause making a call on the deck is as hard as changing a song!
    Ive rigged up amps and speakers and subs and stuff so i know its easy, but ive never encounted this bypass before. I did read that the new decks are more complex in there design and people have simply earthed out the handbrake wire and it still doesnt work..

    Apprently it needs a pulse of signal to activate, hence like the handbrake, when you pull it on that creates the "pulse" as its engaged. However if you took the handbrake off i assume then it would prevent the screen from working. with that theory then if it has a perminent earth then it should work, therefore the pulse thing is BS!

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    Senior Member Thirteen13's Avatar
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    Re-reading the manual it suggests the green wire needs to be connected to the power supply side of the handbrakes.

    Just some further reading into needing a relay, it seems with newer HU's to get around just simply earthing out the green wire, the handbrake safety needs to have no power going to it before it starts up, once the car is running, when it receives the power signal/earth signal (as in from putting the handbrake on) then it says ok DVD ON. Because the Blue/White amp wire only sends power after the deck is started up, thats why this method running off a relay would immitate NO power on start up, AMP Wire gets power, engages relay then adds power to green wire.

    This would suggest that either a manual switch or a relay be used to close and open the earth signal.

    What about using a transistor ?

    Would drawing some of the power from the amp wire into the relay cause problems to power up the amp ?

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    Right, I suspected there might be something like that, it is entirely possible that the time it takes for the relay to energise won't be sufficient for it to detect the change (though most headunits will delay a bit before turning on the amp to prevent thumps and such), best bet is probably a delay relay, actually engages X time after it gets powered, best way to find out is to try it though.

    It is possible to use a transistor of some description for this, though a MOSFET would be a better option, the trick would be making it sufficiently robust, and whether or not it'd have sufficient delay between being powered and switching the handbrake line for it to be recognised (though there are fairly simple fixes for that).

    I'd suggest you "suck it and see" if a standard automotive relay prevents your amp from powering up you can get more sensitive relays from places like Jaycar, you want a 12V coil "reed" relay, though you'll need to be able to solder to use one. They take less current to energise leaving more signal for your amp remote input.

    There is another option using only automotive relays but you'd need 3 of them...

    Mind if I was designing the thing I'd make it ignore any handbrake signal which conicided with the amp remote line going active specifically to "fix" that scenario (though a delay relay will fix that too).

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    Senior Member Thirteen13's Avatar
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    Well ive been doing some further research. Basically most amps need about 20ma to power up. The Amp wire puts out 300ma. So using the relay should take around 100ma and still leave me plenty for an amp.

    what i need to know now is

    just needed some extra advice on this. I want to rig up the Quenching diode to this rig also.

    Would the wiring be:

    Black: 86 + 87
    Blue: 85
    Green: 30

    With the Diode set between 86(anode) and 85 (cathode) ?


    Using the relay method has been proven time over and over to work. So its just a matter of wiring it up

  9. #9
    Senior Member artman's Avatar
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    The remote wire out of the head unit goes to the remote input on the amp, this does not draw much current, no relays required, its basically a signal for the amp to turn on. Then you wire the +ve terminal of the amp direct to the car battery with suitable capable wiring gauge (and fuse as close to battery terminal as possible) and do the same for earth to the amp with decent cable to sound chassis point near amp (no fuse required).

    A nice article explaining relays: Browser Warning

    Cheers

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    Senior Member Thirteen13's Avatar
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    I know how to wire up the amp..... Im not asking about that.....

    Im asking the sequence to attach the spades to the relay and how to lay the quenching diode.

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    Senior Member artman's Avatar
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    Sorry, misunderstood. The article I linked explains the usual relay terminals, 85/86 are the coil, often the relay schematic is shown on the relay too.

    Cheers

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    Quote Originally Posted by Thirteen13 View Post
    With the Diode set between 86(anode) and 85 (cathode) ?
    Diode needs to be reverse biased, i.e. cathode pointing to the positive terminal, assuming that your pinout is correct (I don't remember these things by pin number I look at the diagram on the side of the relay ) you have your diode correctly oriented.

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    Quote Originally Posted by jbrewster View Post
    Diode needs to be reverse biased, i.e. cathode pointing to the positive terminal, assuming that your pinout is correct (I don't remember these things by pin number I look at the diagram on the side of the relay ) you have your diode correctly oriented.
    Going off how i have described the numbers ? The blue/white amp wire i assume supplies the power that connects to pin 85, meaning that i need to solder the cathode onto pin 85 and the anode onto pin 86, as pin 86 has the ground on it.?
    im a bit lost myself I had a laugh

  14. #14
    Senior Member artman's Avatar
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    Why do you need a diode to power the relay?

    If all you are wanting to to do with your head unit remote turn on wire is trigger the relay, wire this wire to one side of the relay coil, the other side of the coil to earth. The relay coil doesn't have a polarity

    Cheers

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    Senior Member Thirteen13's Avatar
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    Quote Originally Posted by artman View Post
    Why do you need a diode to power the relay?

    If all you are wanting to to do with your head unit remote turn on wire is trigger the relay, wire this wire to one side of the relay coil, the other side of the coil to earth. The relay coil doesn't have a polarity

    Cheers
    i want to prevent the back EMF when the coil switchs off so put in a quenching diode

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    Quote Originally Posted by Thirteen13 View Post
    Going off how i have described the numbers ? The blue/white amp wire i assume supplies the power that connects to pin 85, meaning that i need to solder the cathode onto pin 85 and the anode onto pin 86, as pin 86 has the ground on it.?
    im a bit lost myself I had a laugh
    Going off your wiring description, the pins on the relay are irrelevant for the diode orientation (assuming you have the two correct pins for the coil) the cathode of the diode should connect to whereever the blue wire from your head unit connects and the anode should connect to the black wiring.

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    Quote Originally Posted by artman View Post
    If all you are wanting to to do with your head unit remote turn on wire is trigger the relay, wire this wire to one side of the relay coil, the other side of the coil to earth. The relay coil doesn't have a polarity
    As the magnetic field around the coil collapses when the relay turns off it induces a current in the coil, resulting in a negative spike (generally in the vicinity of -400V) back into whatever is driving the relay, depending on what the headunit uses to switch the remote output this sort of back EMF may quickly kill it, by placing a reverse biased diode across the coil provides an alternative path for the spike, thus preventing it from damaging the drive electronics.

  18. #18
    Senior Member artman's Avatar
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    I see, thanks for the info, I have never considered this. I have run a relay off the amps remote lead previously a few times with no issues, maybe those particular decks were not effected.

    Cheers

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    Senior Member noidle22's Avatar
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    i ran 3 amplifiers off a 30A bosch relay and just used the remote trigger wire from the head unit to switch the relay on. ran that setup for about 1.5 years and never had a problem, still using the head unit now on a much smaller setup (one amplifier) and have removed the relay and just use the remote trigger from the head unit straight to the amplifier. still works fine.

    a Pioneer head unit like yours isn't easy to kill, i don't think you'll really need the diode, but if you want it then go ahead.



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