Hello all, I'm new to the BMW scene after owning Audis for 25 years. I just picked up an '06 M3 convertible, and I want to replace the factory nav with something aftermarket. I'm still reading through posts on comparing the options out there, but regardless of what I go with I know I'll have to run cabling from the head unit to the trunk. My car has the H-K audio, if that makes any difference. What I'm looking for is hopefully some sort of writeup or post or video that shows the best way to run cabling from the dash to the trunk. I had a few promising leads that eventually led to 404s here, unfortunately, so I figured I'd be a noob and post a question. Appreciate any help or guidance, I hope someone knows of where I can find this info.

Many thanks!

What do you plan on installing such that you think you need to run cables to the trunk? Do you have the BMW NAV head unit?

 

Yes, BMW NAV head is what I have, and from what I've read that would need some rewiring for the aftermarket heads like the AVANT4 or similar. Am I misunderstanding? (quite possible)

 

The BMW NAV unit has most of the factory electronics in the trunk. If you're going to install a head unit that reuses the factory wiring, amps, speakers, etc. then you would need to run a cable from the replacement head unit to the trunk so that you can interface with the factory electronics. This would be the case with the AVANT4 or Android based head units out in the market.

If you're not going to reuse the factory electronics, then the answer would depend on what you're trying to do.

 

Yes, I intend to reuse the amps and speakers as much as I can. Either way, I'd be looking for the best way to route cabling from the trunk to the head unit location - preferably with some instructions on trim removal, etc, as this stuff is getting a bit brittle at 17 years. I want to make sure to do it right as opposed to trial and error.

 

I guess optimally I'd like to just drop in a head unit, but that only seems to be possible if you have the single-DIN radios, so barring that I'd like to do as little work as possible to get something like an AVANT4 wired in. Which looks to be running cables all the way back. So, just trying to determine the best way to accomplish that without breaking things.

 

I've ran cables from the headunit to the trunk. Best option is behind the headunit to the left past the steering column, underneath the interior trim underneath the door, all the way to the back (behind the rear side panel if it's a coupe). There's a hole behind the back rest of the rear seats which you can fit the wiring through. Same can be done from the right side of the car instead of the left, but I was thinking left since your HK amp is already on the left side in the trunk. If you remove the floor trim below the doors (don't know exactly what they're called), use one of these tools to remove interior clips, and put the tool right underneath the clip. DON'T pull the trim itself, as it will break where the clip sits!

 

This is a good summary so I won't repeat. I suggest you run the cable down the left side of the car because on the right side, there is a heavy 12V cable which can cause interference unless your signal cable is shielded in some way. Avoid removing the door sills as there's a >90% chance you will break it due to age. Just tuck the cable underneath the sill as best as you can. Since you have a convertible, you will need to remove the back seat and tuck the cable behind the side panel and feed it into the trunk via an opening. Here is my son running a cable for the backup camera connected to an Eonon unit. We elected to run it down the right side because it's not an audio signal cable so running it by the heavy 12V cable doesn't matter. Note the wooden dowel we used to fish the wire through the opening into the trunk.

 

Good advice above. If you aren't sure how to remove trim or panels, just look on YouTube. I found what I needed there and managed it with minimal issues.

 

I did it a little different than above. Instead of running behind the dash I ran the cabling (in my case rear camera wire and rca for subwoofer) down through the central console to the crease that runs right under the front seats. From there under the driver seat (had to take the seat out) to the driver side door trim.

Then from there followed the door trim back to the right portion of the rear seat and seat back. Behind the right portion of the seat back there are gaskets with existing wiring that you can route your wires through.

All in all you need to remove the center console, driver side seat, rear seat base and right portion of the rear seat to do this. Also the driver side trunk panel so you can pull out the wire.

I recommend you use automotive wiring tape if you are running more than one wire. There are ample locations to put the wiring in with existing clamps along this route.

Also you explicitly want to run these wires on the driver side as the 12v battery cable is on the passenger side.

I currently have my car apart so I can take some photos if it’ll help you.

 

yes to all above!

run wires down the middle console & thru backseats.. the biggest pain in the ass is putting everything back lol.. but mostly running the wire to between backseat/trunk area.. i rain my pair of speaker wire (16 ga) to new speakers and had them fork left and right... utilizing OEM pass thru in the doors as well! tedious!

 

Thank you so much, everyone! Ok sounds like driver's side or middle console is the approach, possibly under the seat, and like I suspected with as little panel removal as I can manage. Removing the seat is scary, but I'll youtube it, maybe it won't be that bad.

I have a number of console repairs to do at the same time so maybe up the middle is the way - either way I'll report back how I make out. Thanks so much, again, everyone. You make it feel a little less daunting.

 

Removing the seat is 4 bolts and unclipping the cable if you have power seats. Super easy and good opportunity to vacuum 20 years worth of coins and dust down there.

 

I'm looking forward to finding some money, now!

Good point on disconnecting ground, I'll do that as well.