# Jetta mk4 key sense wire



## cdnalpina (Sep 10, 2009)

Hey Everyone,
I was installing an aftermarket stereo in my Jetta last night with a harness adaptor and all went well except the stereo won't turn off when the car is shut down and the key removed.
I did some searching on the topic but I am still not totally clear on something. I understand that the brown red wire is the key sense wire and, of course, the harness adaptor does not have a provision for this. I have seen some people wire up a relay to combat this but I guess my question is can the brown red wire be wired directly to the accessory wire of the harness adaptor? I'm just wondering if there is a more simple solution to this other than running a relay.
Cheers,
Rob


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## CMihalcheon (Jan 29, 2007)

*Re: Jetta mk4 key sense wire (cdnalpina)*

All you need to do is run the ACC+ wire from the aftermarket HU harness adapter to the key sense wire. No relay required


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## cdnalpina (Sep 10, 2009)

Great - thanks so much for the reply!


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## cdnalpina (Sep 10, 2009)

*Re: (cdnalpina)*

Sadly - that did not work. I don't know if it is because the car is a 2003 or what but it looks as though I am going to have to go the relay route.
Cheers,


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## CMihalcheon (Jan 29, 2007)

*Re: (cdnalpina)*

it should absolutely work on a 2003. Where do you have all the wires from the HU wire harness going?


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## cdnalpina (Sep 10, 2009)

I color matched all the aftermarket stereo wires to the wires on the harness adaptor. What I changed last night was to connect the red brown wire of the harness adaptor to the ACC wire from the head unit. So the red wire on the harness adaptor was left unconnected after that. When I did this, there was no power to the deck at all. Is that what you meant I should do?


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## CMihalcheon (Jan 29, 2007)

*Re: (cdnalpina)*


_Quote, originally posted by *cdnalpina* »_I color matched all the aftermarket stereo wires to the wires on the harness adaptor. What I changed last night was to connect the red brown wire of the harness adaptor to the ACC wire from the head unit. So the red wire on the harness adaptor was left unconnected after that. When I did this, there was no power to the deck at all. Is that what you meant I should do? 

You can't do this on a VW!!! only the speaker wires, constant power and ground can be connected to the stock harness. Disconnect the rest right away, as two of the wires are for the cars diagnostic system, and if connected to the stereo when you have the car scanned will fry the scanner. The switched power wire and dimmer wire need to go to other power sources in the car as well. Dimmer goes to the back of the dash lights adjustment switch, middle wire (just splice it in). Switched power goes to either the 75x terminal or key sense wire.


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## cdnalpina (Sep 10, 2009)

*Re: (CMihalcheon)*

Wow - good to know thanks!
what I have hooked up are:
all the speaker wires
ground
constant hot
acc
blue remote wire
So I will disconnect the blue wire and the acc wire. Thing is, when I connected the acc wire to the key sense wire nothing turned on at all - so I am at a bit of a loss here. I don't need a dimmer wire for the head unit I have. So, basically I need to sort out the acc power to the head unit and the key sense wire. Does that sound correct? 
I found this thread:
The OEM radio is turned on by the CAN bus. The ground is pin 12, the BAT is pin 15. There is no accessory to turn off the aftermarket radio, but you have three choices.
Using Metra 80-9003:
1. Hook up the accessory of the radio to the vehicle ignition. Pretty easy and there is a stud underneath the dash.
2. Hook up a relay to the key sense wire (18g brown/red) located in the steering column. You will hook up pin 30 to the red/acc wire; pin 87 to the BAT/yel wire; 85 to ground; 86 to the key sense wire. This lets you use the radio with the car off, but will obviously turn off the radio when you remove the key.
3. Use Metra XSVI-9003 for 2002 and newer cars. It uses a circuit to interface with the CAN bus to turn the radio on. Simple to install, and includes an illumination wire to control a deck's lighting. Will keep the radio on until you open a door and remove the key, but you cannot just turn on the aftermarket radio just by pushing a button in. You still have to enter the key.
http://enfigcarstereo.com/shop...3.jpg
Which is where I got the relay idea from. So what would be your suggestion? I apologize for all the questions - I am fairly decent electronically, but I have not had to deal with key sense type systems before.
Again, many thanks for your help.
Rob


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## CMihalcheon (Jan 29, 2007)

*Re: (cdnalpina)*

the ignition stud under the dash is the 75x terminal
hmm the key sense wire should be working for you. Possibly try testing it with a multimeter, if not go off of the 75x terminal.
and make absolutely sure no other wires are connected to the cars wire harness through the harness adapter. I cut back all the wires I wasn't using to make sure, and to reduce the space the adapter took up


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## blazerpounds (Mar 19, 2008)

key sense does not supply enough current to keep the radio on, thats why you need a relay. I think the keysense is only 5 volts...


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## cdnalpina (Sep 10, 2009)

*Re: (blazerpounds)*

Thanks guys. I pulled it all apart yesterday and connected the accessory wire to the 75 stud - all is well. 
A point of note, in the factory harness (on my car) there was no pin receiver (and hence no wire) in the key sense wire position. I used a multimeter on the factory harness and played with turning the car on and off, and key in and out. The only thing it yielded was a constant hot or nothing. Not sure why that is but I now have a stereo that functions properly so it's all good.
Cheers,
Rob


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## forumaccount (Jul 24, 2012)

blazerpounds said:


> key sense does not supply enough current to keep the radio on, thats why you need a relay. I think the keysense is only 5 volts...


 I know this is old old old, but shouldn't the key sense just act as a switch (acc wire) which basically signals the unit to turn on/off while the unit gets its power from the constant power wire (12v+)? Or is the constant power wire the low voltage wire which keeps memory from erasing? I can't remember, it's been 2 years since i wired mine . All I know is i have a fused wire from the 75x, a ground, and something else :\. Looking to get mine hooked up to the key sense though.


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## NFrazier (Jul 22, 2006)

forumaccount said:


> I know this is old old old, but shouldn't the key sense just act as a switch (acc wire) which basically signals the unit to turn on/off while the unit gets its power from the constant power wire (12v+)? Or is the constant power wire the low voltage wire which keeps memory from erasing? I can't remember, it's been 2 years since i wired mine . All I know is i have a fused wire from the 75x, a ground, and something else :\. Looking to get mine hooked up to the key sense though.


 No. The keysense wire lacks the current needed to turn on and keep the radio on. 

The Constant wire is for the radio to retain memory (presets, clock, settings, etc.). 

If you want to maintain the key sense portion (i.e., turns on and off with keysense), you'll have to use a relay.


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## forumaccount (Jul 24, 2012)

NFrazier said:


> No. The keysense wire lacks the current needed to turn on and keep the radio on.
> 
> The Constant wire is for the radio to retain memory (presets, clock, settings, etc.).
> 
> If you want to maintain the key sense portion (i.e., turns on and off with keysense), you'll have to use a relay.


 This makes much more sense, thanks.


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## 1.8terminator (Mar 24, 2011)

Sorry to bump this but I need some help I picked up an 03 Jetta for 300 with some electrical bugs the main bug is that the accessory lights don't shut off when connected to a battery I'm noticing a ratty sound system wire install do you think they messed with light switch wiring or something worse any suggestions would help

Sent from my XT901 using Tapatalk


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