angeloxnet

So i'm hard wiring stuff to the rear SAM, found the "12v" red cable plugged into the SAM which appears to have constant power even when the car is off and locked.

Great I thought, but after about an hour my device no longer has power.

Is there some kind of cut-off or power saving feature on Mercedes cars (specifically an 2008 W204) that cuts power to rear SAM after a period of time? ie. 1 hr

I know I get power for about 1 hour after the doors are closed and locked (confirmed with a LED light tester)

Looking for some insight...

RLE

I think you have gotten into the one hour timed circuit for the green escape button on the inside of the trunklid.

There is switched and un-switched 12V in the fuse panel on the right side behind the little door.

angeloxnet

It's the big red cable i tapped into. It plugs directly into the REAR SAM itself.

RLE

Well, ask yourself, what electrical device in the back is timed.

The green button.

Keep testing.

angeloxnet

I have tested and tested for several days now, can you gave me an example of what cable you think has constant 12v? That would be helpful

Do you know for certain the big red cable plugged into the top of the rear sam is the "emergency button"? For a flashing LED, it doesn't seem like it would be. Also if you look at the entire sam assembly there is only 1 source coming into the SAM, which is the red cable I mentioned.

RLE

That green button would have a small 12v wire plus ground. I don't know anything for certain because I haven't looked. I'm just using normal electrical troubleshooting procedure.

But I do know about about the fuse panel on the right and have used it for my backup camera power, long ago. The SAM is on the left side and I'd be cautious doing any testing on it because they are expensive.

Just check all the unused fuse holders with the key on and then off.

angeloxnet

I've retrofitted my backup cam, my 2012 tail lights, and OEM sirius satellite radio myself so I'm familiar with the SAM, I know the 2 fuses on the far right are for front and rear cigarette lighter/socket.

I just went into my garage again and the green button is definitely not the same BIG red wire feeding into the SAM.

Big Daddy

Perhaps they remove power to prevent the battery going flat when the car is not used for a long time. The SAM is not the place to connect other pieces of gear to. They are very fragile and will die if not treated carefully. Their funeral is expensive. If you are plugging or unplugging anything into the Sam disconnect the battery first

angeloxnet

Here is an update.

I spoke with a Mercedes technician who is a friend, and he confirmed that the rear SAM power is linked to a relay that has a timer, that actually fluctuates based on temperature outside, so it will cut power after 45 minutes to a 1 hr.

mangoango

iTrader: (1)

That's interesting. Thanks for updating the thread with that. It might help somebody else in the future.

RLE

Did he say what the purpose of this might be?