W245 No ignition switched wire

[damjandim]

I've bought a Bluetooth module which connects to the AUX port in my B-Class W245 2005, very similar (if not identical) to this one. As per the instructions, the bluetooth module's 12V wire needs to be connected to an ignition switched 12V wire from the car. Well, it appears there is no such wire behind my radio and AC controls panel. Here's the type of radio I have:


I've checked all of the pins of the radio connector, and none of them appear to be ignition switched. I did find two pins which had 12V with the ignition off (I guess that's why you can turn on the radio even when the ignition is off), one of which dropped to 4.6V when the ignition is on. Then I moved on to try and leech of of the AC controls unit, again with no luck, as I couldn't get my multimeter probes inside the connectors for it (the pins are really tiny on that one). I think the AC control unit might have an ignition switched wire, because it's lights come on only after ignition if I'm not mistaken, but I have no way of identifying it. Any ideas on how to find a switched 12V wire somewhere inside the central panel?

 

[GLK]

Power socket is your best bet. Easy to get to, easy to route the wire up (or down, as the case might be - I had my bluetooth in the power socket tray).
If it's cigar lighter, rather than a power socket (i.e. non-smoking option), then don't use the middle wire - it's for the tiny light).
Don't forget inline fuse.
Wouldn't try to power gadgets off an A/C controller, or OCP (like some use for dashcams) etc, etc - not meant to be used like that and messes up with diagnostics.

 

[damjandim]

Hey @GLK, thanks for the quick reply. I do have the lighter, so thanks for the heads up for the light Maybe while I'm there I’ll check and see why that’s not working as well.
More importantly, regarding the inline fuse you mention, do you mean I should wire in a fuse between the 12V ignition-switched wire and the bluetooth module? If so, which amperage should I choose and can I use a standard car fuse, like the ones found in the fuse box?

 

[GLK]

No worries
I always fit inline fuses (the waterproof type is the best) for all the gadgets I fit, and I had a lot in my old A200 C169
Anything around or under 3A will do.
Here's a couple of WIS files to help you get to the power socket / lighter.
I had a non-smoker package in my old car, so retrofitted a blue LED light where ashtray light was supposed to be (don't know why Mercedes think us non-smokers don't need to see what's inside the tray

 

[damjandim]

@GLK Thanks for elaborating, those docs will come in handy as well. I'm currently waiting for some trim removal tools to be delivered, so I can stop using a kitchen spatula to do the job (I've pushed my luck with it twice already). As soon as they arrive, I will do the job and post some feedback photos here about how it went.

 

[damjandim]

Hey @GLK , I’ve just now been able to turn my attention to this project, and I’ve run into a bit of an issue. I dismantled the cigarette lighter area as per your instructions, and got to the wires powering it. There is a brown wire which is the live one and there is a green wire which is the ground. There is also a much thinner wire running along with them in the cigarette lighter connector which I guess is for the little light in there.

I spliced my bluetooth device onto the brown and green wires accordingly, and measured the voltage between them and it’s at 12.3V when the ignition is on. I also tested the lighter and it works properly. However, the bluetooth module doesn’t turn on (it has a little power status LED on it).

I took the bluetooth back home and connected it to a 12V DC adapter in the house and it works properly. I measured the voltage of the adapter I used at home, and it’s a bit below 12, something like 11.5V.

The only difference between the two setups (car vs home) I can see is that one is at 12.3V and the other is 11.5V. Do you think that could be the problem, or do you maybe have another idea?

 

[Ted]

I would check your supply wires again as I would expect the brown wire to be the earth.
The illumination wire will probably be mainly grey with a tracer colour.

 

[damjandim]

After I wrote the reply, I thought to myself: "the brown is probably the ground then, you dumbass" as I realised I never tried switching the wires around. Oh well, hindsight is 20-20, I'll try again tomorrow and post back

 

[GLK]

As above - I'm sure I wrote about this same thing (power socket wiring) very recently somewhere: green/black is 12V positive on circuit (terminal) 15R, i.e. ignition on; middle wire is the light, brown is, as always (well almost) is ground.

 

[damjandim]

Hey everyone, the project is done! Switched the wires around and everything was fine, of course. Here’s a quick rundown of my build:
1. Connected a blue Mini ISO jack to the back of my Audio 5 stereo, which has an audio cable leading out of it, ending in a female 3.5mm jack.
2. Connected a male to female 3.5mm splitter, so I got two female jacks available for connecting the bluetooth module in one and an aux port in the other.
3. Made a female aux port inside the little shelf below the heating controls (see first photo), which has a male jack on the other end which goes into the splitter.
4. Put the bluetooth module below the lighter/socket module, just kind of tucked it between the wall of the center console and the foam surround of the gear-shift lever. Connected its power cables to the cigarette lighter (see other photos) & replaced the little bulb on the cig lighter while I was in there and repaired its contact strips which were bent for some reason, and connected its audio output male 3.5mm to the splitter.

If anyone’s wondering why I added both an AUX jack and a bluetooth module, I don’t really have a straightforward answer other than because I could I thought to myself while I’m in here running cables, why not jam an AUX in there as well, it’s not much added effort and price, but offers a nice clean alternative if the bluetooth should ever fail or if I’m not happy with the sound quality. Also I’m a bit worried what would happen if I ran the bluetooth at the same time as some other device is plugged into the lighter jack, like a refrigerator when I do camping or a phone charger, so I wanted to play it safe.

Anyway, thanks for the help, and hit me up if you have any

P.S: Please excuse my manky car interior, I sent it to get a wash as soon as I finished this thing

 

[GLK]

Great result and looks good too