For FAQ: Interior Hardwiring - Gauges Radar Detectors Neons Lights Boost Pressure Ipod 12v Dimmer

[rs4-380]

The following post will detail how to pick up +12v, switched 12v, dimmer and Ground inside the cabin of the car without hacking into wiring and compromising the OEM fusing system. This can be used for anything that requires 12v. Gauges, radar detectors, interior lights, ipod chargers, cell phone chargers, etc. etc. etc.

First thing, decide whether you need switched 12v or +12v (always on). Most applications will choose to go with switched 12v so your device will turn off when you turn the car off. Some people may choose the capability of operating their device with the car off, and still some may need a switch 12v and +12v source.

First off, disconnect the negative battery cable. You will save yourself headaches trying to find blown fuses after you short circuit something, because you will short circuit something.

To start, you need to remove the plastic panel beneath the driver side dashboard, and the plastic fusebox cover on the drivers side of the dashboard. use Gary's interior disassembly DIY's to do this.
( --steps 43 to 48).

Look up under the dashboard at the fuse panel. You will see several threaded connectors here. This is where you will get your 12v sources and ground. The stud marked 75x supplies SWITCHED 12v. The studs marked 30 (either one) will supply CONSTANT 12v. You can pick up a ground on the stud marked GND in the picture, that secures the fuse box to the bracket. Use appropriate sized crimp on ring terminals )found at any local autoparts/hardware store) to fit over the studs. PLEASE PLEASE PLEASE do not just dtrip the wire and stuff it under the nut, and then tighten the nut down. This is ghetto. Ghetto is bad. Ghetto and 12v can cause fires. Also, it is EXTREMELY recommended that you fuse your 12v source, whether it be switched or constant. You can do this with a simple in-line fuse holder, again available through any auto parts or hardware store. 10 amps fuses should be fine for any gauges, radar detectors, or chargers. For lighting just divide the TOTAL wattage by 12 and then move up to the next highest amp rating (ie total of 100 watts, 100/12 = ~8, so use a 10 amp fuse). The reason for fusing here, is because these feeds are protected by the metal fuses on the battery. Not only are these fuse more difficult to find then common AGC's or ATO's, but they have much higher ratings because the are main line fuses, which means that your device can possibly be damaged before these actual fuses blow. By using an appropriate sized dedicated fuse in your 12v line, you avoid this problem.

To tap into the dimmer circuit for gauges, etc. Remove the wiring harness from the back of the dimmer switch (you meay need to remove the headlight switch to get room to move around). The blue/gray wire is the one you want to tap into for the positive side of your lighting circuit (with most bulbs it doesn't matter which is positive and which is negative though). I personally hate the crimp-lock style connectors, and prefer a butt splice connector (one side of the dimmer circuit and the feed for you lighting go in one side, strip the other side of the dimmer circuit longer then normal, double it over, and stick it in the other side), but it's up to you what you use here. Again, hardware store, or autoparts store can help you get what you need. For the negative side of things, there is no need to tap into the brown wire. Ground is ground, and you can just use the same stud on the fuse panel, or forget about running another wire, and just tap into the ground you already ran close to the device (again, no twisted wires and electrical tape please).

To run wires/boost tubing to the engine compartment, you can use the existing grommet/hole above the accelerator pedal. If you have a drive by cable car (early 2.0s and a handful or VR's) this will be occupied by the accelerator pedal. Don't just knock out the grommet and lose it. Push it through from one side, and the slice a small cut in the middle of the rubber. Then run your wires/tubing trough the small slit, the rubber should provide a seal around your wire/tubing. The carefully push the grommet back into the hole (make take a couple of times before you can get it seated without pushing it through). Before feeding your wires through the grommet, wrap them in electrical/chafe tape for chafe protection. The blue/white wires and black tubing go through the grommet in this picture.



Modified by rs4-380 at 10:49 PM 6-20-2006

[LSinLV]

we love you Dave!!

...a new DIY!!!

[AutoTastC]

You never post anything that is not a contribution to you

[VDub GTI]

[Dubsport Inc]

No disrespect but dimmer is gray/blue not blue/gray.
HTH
Richard

[rs4-380]

Quote, originally posted by Dubsport Inc »

No disrespect but dimmer is gray/blue not blue/gray.

no comment

[dieselgti]

Nice work!

[wzcunningham]

always giving back to the community...

[aslaveofaudio]

is the dimmer wire voltage controlled by the dial that is used to dim the dash lights or is the one that automatically dims when you lock the car?

thanks. useful diy btw; i like ur wiring a lot more than shoving the wires into the fuse panel solution.

[rs4-380]

Quote, originally posted by aslaveofaudio »

is the dimmer wire voltage controlled by the dial that is used to dim the dash lights or is the one that automatically dims when you lock the car? thanks. useful diy btw; i like ur wiring a lot more than shoving the wires into the fuse panel solution.

the dimmer circuit voltage (instrument panel, switches, radio, climate control lights) is controlled by the dimmer switch. The overhead lights (which dim when locking the car) are controlled by an entirely different circuit.

[dremhmrk2]

Great Thread

[03GLXVR6Jetta]

Dave, thanks for the thoroughness!

Can I use that blue/grey dimmer wire for the illumination wire coming out of my HU (Pioneer DEH 7800MP). I assume it'll get it's grounding via the HU.

Thanks

[rs4-380]

Quote, originally posted by 03GLXVR6Jetta »

Dave, thanks for the thoroughness! Can I use that blue/grey dimmer wire for the illumination wire coming out of my HU (Pioneer DEH 7800MP). I assume it'll get it's grounding via the HU. Thanks

yep, but you should already have a dimmer wire in the stock radio wiring plug. No need to go and splice at the dimmer switch.

[Matt4x4]

You can also tie into the dimmer wire at the ashtray - one screw and it's out, nicely located in the center of the car for just about any mod, if you use LED's, they don't put strain on the circuit, I used this location for a custom aftermarket (lighted) cupholder I mounted next to the hand brake since the afterthought in the dash should NEVER be used.

[4cid]

Quote, originally posted by rs4-380 »

yep, but you should already have a dimmer wire in the stock radio wiring plug. No need to go and splice at the dimmer switch.

whats the color of the HU Illumination cable ?

[BUJonathan]

Quote, originally posted by rs4-380 »

yep, but you should already have a dimmer wire in the stock radio wiring plug. No need to go and splice at the dimmer switch.

I thought there was no provision dimming in the MKIV DD monsoon harness?? I thought dimming along with turning off the stereo was done through the CAN line?

One other question: When tapping into the Power Center (75x) under the dash for accessory power on an aftermarket head unit, is it neccessary to still install an inline fuse, since the stereo has 10 AMP fuse in the back??

Consider me slightly ignorant on the "best practices" of automotive wiring.

[Galacius29]

dumb question i know, but how do you fuse something, is there a diy on it?

[bigmak]

Quote, originally posted by Galacius29 »

dumb question i know, but how do you fuse something, is there a diy on it?

splice in an inline fuse on the power side, not the ground side obviously.

http://42draftdesigns.com/electrical_fuses.htm

[redfred18T]

that's an excellent diy, I wish I knew that like 2 years ago

I still think I will put it to good use

[jhirsch123]

Can someone tell me what size eye ring to use to tap into the 75X? I'm using 14 gauge wire but can't quite tell and would like to know before I take the dash apart

Great thread

[rs4-380]

Quote, originally posted by jhirsch123 »

Can someone tell me what size eye ring to use to tap into the 75X? I'm using 14 gauge wire but can't quite tell and would like to know before I take the dash apart Great thread

I want to say you should be fine with a 3/8" (id) ring terminal.

[vwboy308]

good stuff

[dremhmrk2]

I wish I didnt use crimplocks on my dimmer wire, but I didnt see any other solution... I would love to make a splitter coming out of the dimmer, sort of like a repair wire but with 2 wires coming out so I could then route one to a fuse/distribution block. Right now I have a tree coming off my dimmer switch, for the W8 and my perfect match LEDs

[JettaJensen]

From the dead like whoa.

[JettaGLI18t]

I'm going to be hooking up a power inverter (175watt), at this same place as the pictures above... it has the lighter jack hook up now. I am going to be cutting the wire and adding an inline fuse (15 amp). If I need to extend my power and ground lines, beyond the inline fuse, what gauge line would I need?

[McFly.]

useful

[andrius]

Flawless! Thanks so much for this! I am a novice and had never installed an XM Radio (Delphi Roady XT) or anything with direct power. The directions were perfect! I successfully installed a direct-line power kit and FM Direct Modulator purchased from myradiostore.com.

The interesting part was that when I pulled out the older Delphi Roady2, the installer had tapped the ground from the ventilation switches and tapped the power from the radio harness, using the "ghetto" wrapping-the-wire and then taping it up. I assume that method would not be recommended.

The full removal and re-installation took me a little over 3 hours, with most of the time removing and re-installing the trim paneling.

Thanks again!

[RedSled]

subscribing to hardline my passposrt 8500 X50 this weekend

[MK4WolfsburgJetta]

Is there any way to turn off the motor, but keep the gauges on untill you remove the key from the igniton? Just like a CD player. Thanks all help appreciated!

[MK4WolfsburgJetta]

Found it! You can tap into your switchable 12v source on the CD player. When you turn off the key everything stays on till you take it out, and its a super clean wire job.

[Macks04GLI]

Do you have a pic of where you found the switchable 12v on (i'm assuming) the factory radio?

[BADBOYJT]

i'm trying to figure out which wire to use for the amp remote turn wire. the one from the stereo i accedentlay ripped out. i'm gonna be hooking it up to a switch.

[rs4-380]

Quote, originally posted by BADBOYJT »

i'm trying to figure out which wire to use for the amp remote turn wire. the one from the stereo i accedentlay ripped out. i'm gonna be hooking it up to a switch.

it you are going to be hooking it up to a switch I would feed the switch with ignition switched 12v, that way if you forget to turn off the switch, the amp will still turn off when you turn off the car.

[dubjager]

sweet, very helpful!

[gtiiiiiiii]

Quote, originally posted by Macks04GLI »

Do you have a pic of where you found the switchable 12v on (i'm assuming) the factory radio?

Yeah I really would like to know this also. I'm installing a parrot blue tooth kit and need a 12v switched ignition source. I'd prefer to just splice into one rather then hooking up a terminal end.