[kaboom28]

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?

 

[kaboom28]

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.

 

[kaboom28]

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.

 

[kaboom28]

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.

OP, make sure you disconnect battery ground before working. There are electrical plugs for sensors and airbags that you MAY have to unplug depending on your wire routing so you want to avoid getting a code or otherwise screw something up.