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Discussion Starter · #1 ·
How’s it going everyone. I’ve searched everywhere for answers but I can’t find anything clear and to the point so this is my last resort. I replaced the monsoon head unit but I noticed a blue plug in the factory harness that connects to nothing in the aftermarket harness.
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does anyone know what this is for? I disabled the preamp in the aftermarket head unit and the result was no sound. I was confused because I would think the monsoon amp in the trunk would provide the speakers power. When I turned the preamp on I got sound. I still need to check what all speakers were working (4 door speakers and tweeters). Curious if that blue harness is for the monsoon amp. Another thread said the yellow wire on the aftermarket harness was for the monsoon amp.
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now I’m just confused. The other issue is why does the aftermarket harness have a blue amp remote wire? Is that the wire for the monsoon amp? If it is then which wire should I connect it to on the stereo harness? Another thread said to wire the red 12v ignition wire on the stereo harness to the yellow 75x nut under the dash. Should I connect the blue amp wire on the aftermarket harness to that same nut under the dash as well? My subs amp remote wire is connected to the remote wire on the stereo harness. Any help is greatly appreciated.
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For the aftermarket wiring, you have to find the aftermarket installation manual.

For the factory wiring, go to the MK4 forum.

Golf IV & Jetta IV | VW Vortex - Volkswagen Forum

It would also help to buy the Bentley manual for your car and learn how to read the Current Flow Diagrams (wiring diagrams)

VW - Volkswagen Repair Manual: Jetta, Golf, GTI: 1999-2005: Service Manual - Bentley Publishers - Repair Manuals and Automotive Books

It's also on eBay but the one I saw didn't say it was two volumes.
 

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Hey i posted that comment about wiring to 75x.

I had an 03 Wolfsburg with the monsoon system and I don't recall seeing that blue plug back there but this was 7-8 years ago. the reason why i connected to 75x was because the radio would never turn off if I connected it to the 12v off of the radio harness even if I took the key out and locked the car. I remember 2002.5+ models had added something to the canbus system that made wiring radios a little weird not sure what it was but the general consensus was to just wire it to 75x to turn on and off with the key.

the blue amp remote wire you are referring too I connected my amplified antenna too, because none of my radio stations would work with the aftermarket radio, so I got an amplified radio antenna adaptor from enfig and wired it to the blue remote wire and it worked perfect.

for my subs, I also connected the remote wire to 75x and put an inline fuse on both connections
 

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Not 100% sure about the Monsoon system, but on all VWs I've replaced stereos on, that blue plug has always been for an aux CD changer (or sat radio tuner). Check the glove box or trunk to see if there is a prep for CD changer, that's probably where that leads to.
 

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Discussion Starter · #7 ·
Hey thanks to everyone for the info. Turbosharef you are awesome. I got the antenna adapter and didn’t get any signal. The blue wire makes sense. As for the blue plug, it is for a disc changer that is currently gone. I picked this MK4 up for 2 grand. It was not in good shape at all especially the interior. It was a fun project over the weekend though. I have two doors left to reupholster. The stereo sounds great. I replaced all of the speakers and added 2 2000 rms subs in the trunk. I’m only pushing 1200 rms to each of them. I’m getting too old for the bass but it brings back memories. I was going to give it to my son but now I have second thoughts lol.
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