W204 Permanent (unswitched) 12v supply for head end stereo

[omega1]

Hi all,

I am looking for the nearest permanent/unswitched 12v source for an aftermarket head end audio unit.

The device I have requires a permanent 12v source as well as a switched feed.

I have tried the cigar lighter but it also appears to be switched.

In a w204 (2010), where is the nearest supply that I could use, or where is the nearest fuse box and how to get to it?

Thanks in advance!

 

[richard]

The power feed to the existing head-unit is un-switched. Get the switched feed from the cigar lighter (with an appropriate fuse if the stereo doesn't have a fuse on it's loom)

 

[moonloops]

Also, it's sometimes just easier to run a new wire direct from the battery.. just make sure it is fitted with a properly rated fuse.

 

[omega1]

The power feed to the existing head-unit is un-switched.

I actually thought that may be the case, as it seemed to stay powered after taking the key out, but then I thought it may just be a time switch (after taking the key out and locking the car, etc...).

Thanks.

 

[omega1]

Hmm, just gone back out to it and there is no 12v until the key is put into ignition, so it must be switched somehow?

Is it configurable?

 

[Chrishazle]

The only one I've found in my S204 is the phone pre-wired thing in the centre arm rest - my phone starts charging as soon as I clip it into its cradle, whereas all the other points (glovebox Ipad pre-wire, cigarette lighter and the one in the rear luggage area) all need ignition on to be live. Comand also switches off as soon as I remove the key from the ignition, but will stay on for a while if I switch the engine off but leave the key in place.

 

[Diesel Benz]

The only one I've found in my S204 is the phone pre-wired thing in the centre arm rest - my phone starts charging as soon as I clip it into its cradle, whereas all the other points (glovebox Ipad pre-wire, cigarette lighter and the one in the rear luggage area) all need ignition on to be live. Comand also switches off as soon as I remove the key from the ignition, but will stay on for a while if I switch the engine off but leave the key in place.

Your COMAND will have permanent power even if it is switched off immediately when you switch ignition off.

Hmm, just gone back out to it and there is no 12v until the key is put into ignition, so it must be switched somehow?

Is it configurable?

Where is your "there"? As Richard said, the OEM head unit has constant power feed. Can you state wire colours, which connector?

 

[omega1]

"There" is on the the main ISO type connector that plugs into the back of the Audio 20 unit.

The cable colours are red and brown.

The 12v definitely disappears after a while, not sure how long, haven't timed it.

 

[Diesel Benz]

"There" is on the the main ISO type connector that plugs into the back of the Audio 20 unit.

The cable colours are red and brown.

The 12v definitely disappears after a while, not sure how long, haven't timed it.

Strange, seems they have changed it from circuit 30 to circuit 30g. Should never assume the same implementation as for earlier/other models.

Seems you need to feed a new wire from the front SAM.

 

[omega1]

Seems you need to feed a new wire from the front SAM.

Could you please give me an idea of where to locate this, or the closest fuse box to the head end unit location?

Thanks in advance.

 

[Diesel Benz]

The fuse box closest to the head unit (radio) is probably the front SAM. I guess some 204s had a fuse box at the side of the cluster, not sure and don't have to time to check it at the moment. Someone might be able to point a circuit 30 power source closer to the radio?

 

[omega1]

Hi,

Funny you entire the side of the cluster, I followed the booklet and took off a panel to the right of the cluster (between the cluster and the driver door) but there was nothing there. ..

 

[Ted]

Are you 100% there is no permanent live feed?
Most radios need one to maintain station memory.
Also, try holding the power button with key out to see if the radio powers up. If it does, you definitely have a permanent live there.

 

[omega1]

100% sure. I have tested it and there is no 12v present on the red/brown cables on the ISO type connector after a period of time after the key is removed.

Can anyone point out where there nearest fuse box is?

 

[Diesel Benz]

Actually most modern radios do not need permanent power to store radio station info etc. They have EEPROMS that do not loose the content when power is switched off.

omega1, have you considered feeding 30g for both power wires of your new radio? The disadvantage would be that you cannot turn the radio on when parked & ignition off.

 

[omega1]

Actually most modern radios do not need permanent power to store radio station info etc. They have EEPROMS that do not loose the content when power is switched off.

True, the one I have doesn't lose any settings when the power is removed.

omega1, have you considered feeding 30g for both power wires of your new radio? The disadvantage would be that you cannot turn the radio on when parked & ignition off.

I'm unsure what 30g is, but I already have it powered from the switched supply, but would really like it unswitched.

Can anyone point me to the nearest fuse box or source of unswitched 12v supply in this model?

Thanks.

 

[Diesel Benz]

Front SAM must be the closest fuse box to the radio. The attached photo is for a LHD car.

According to the fuse diagram circuit 30 would be available from the upper control panel but I think the wiring diagram said 30g. The fuse is too small anyway (and the wiring).

 

[richard]

More and more of the electronics in Mercs has it's power removed a few minutes after closing/locking the car. "Status" is held in eeprom/flash-memory so the control units don't forget - This (I guess) guarantees the battery won't go flat.

It looks like your W204 does cuts the power to the head-unit after a while too !

Cheers

Richard

 

[Chrishazle]

Just to add to what I said earlier - most Sunday mornings I'm to be found sat in the car reading the Sunday paper while herself is at church (I'm a heathen!!). I leave the key in the ignition so I have the radio. After a certain period of time I get a message on the main screen along the lines of "start the car or Comand will shut down in ... minutes". I turn the ignition on (without starting the car) then off again and the message goes away until that certain period has passed again. As soon as I take the key out of the ignition, Comand (radio, whatever) shuts down.