# Dimmer wire in MK4



## daves_1.8t (Jun 3, 2008)

Hey guys, just doing some research before trying to install my hu.
on an MK4 Jetta 2002. Do I have to connect my illumination/Dimmer from the radio? If I dont will it still work but just at its brightest. 
I know the car gets switched 12v and Dimmer from the Can Bus line which I can not use so the switched 12v and Dimmer need to be wired seperately, Is the only place to tap into this at the Dimmer Control Unit next to the headlight switch?
Thanks


----------



## Kerosel (Jan 10, 2002)

*Re: Dimmer wire in MK4 (daves_1.8t)*

Hi daves. I'm by no means an authority, but I have a bit of electrical knowledge under my belt, and just swapped my factory Monsoon with an OEM Navi unit a few days ago, so stuff is still fresh in my mind.
First, GoMobileR32's DIY thread for the AVIC-D3 is a good source for finding wires.
http://forums.vwvortex.com/zerothread?id=3134807
Switched 12v is pin #1 at the headlight switch, dimmer control is #17 (grey/blue). GoMobile makes the good point that if your head unit is expecting just a non-variable signal to tell when the lights are on, you should use the grey/purple line (he doesn't give a pin number) instead. I've read some threads about people's head unit freaking out if it gets a low (dimmed) illumination signal.
Also in GoMobile's install, he shows the wire to tap for the S-contact instead of just straight 12v switched. The S-contact goes hot when you turn the key, but stays hot until you take the key out, where the 12v switched will go cold when you turn off the ignition. If you tap the S-contact line instead of switched 12v, your head until should stay on after you turn off the engine, remaining on until you pull out the key, just like the factory radio. It _should_... I make no guarantees.








You can tap the S-contact line at the steering column like he illustrates, or someone else in this subforum pointed out that line is also available at the fuse block.
http://forums.vwvortex.com/zer...75714
I elected to tap from the fuse block to make it look a little cleaner. It's the brown/red wire going in, and I believe yellow/red coming out. Tap the one coming out, so you get the fuse in the line for protection, just in case. Going to the fuse box is a little more work, but not impossible.
I hope some of this helps you get started. And good luck with the install if you decide to go ahead with it!


----------



## daves_1.8t (Jun 3, 2008)

*Re: Dimmer wire in MK4 (Kerosel)*

sounds good but I dont want to cut any wires at all so the ignition wire is out of the question. How does the 75x contact work...what is it intended for, what does it do and will it power my radio. I am under the impression that it will work fine and that I just will loose the key in radio on feature with ignition off...i am ok with that. But will my radio work when the key is moved to acc....if i tap into 75x.


----------



## blazerpounds (Mar 19, 2008)

why are you scared to cut wires?
The 75x terminal supplies 12v to anything else that needs it in the car when the key is switched on. It will provide juice to turn the stereo on.
If youre scared of doing this I have the correct can-bus harness Ill sell ya for 70 bucks shipped and brand new, 10 bucks cheaper than enfig. I think ive got 2... maybe three.


----------



## Kerosel (Jan 10, 2002)

*Re: Dimmer wire in MK4 (daves_1.8t)*

Eh, you don't have to cut... use the ubiquitous ScotchLok wire taps. That's what I did. They're designed to slice down through the insulation to make contact with the wire, but not cut the wire at all.
75x is the accessory cut-out circuit. It's like 12v switched except it also goes cold when starting the engine (cuts out accessories to reduce electrical load during starting). If you can live with that, it's not a bad place to go.


----------



## Jmode (Jan 18, 2021)

I know that this is an old thread and not many people need this info anymore, but I just went through this and wanted to add 2 cents.
You don't need to alter the key sense wire at all if you remove the plug from the back of the ignition switch and (properly) pull out the metal contact. Then you hook the wire up to that. It's a bit of work, but could be worth it for you.
Also, if you want to hook your switched power wire to a source that drops power while starting. You can avoid loosing power by getting a timed relay. Just make sure that you get the one that stays on (for a set time) after power is shut off, NOT the one that stays off (for a set time) after the power is turned on. Got mine for about $20 off of ebay. It allows me to set it anywhere from 3 seconds up to a few minutes.


----------

