Plato

Rear sockets only work when the ignition is switched on. How can I make them work when the key (button) is in the first position?

BOTUS

by rewiring the car - were you expecting some magic words ?

Plato

No You don't need a rewiring. If I go trough hardware solution there are two relays in rear SAM (one for the socket another for cigarette lighter) so you just need to change signal for them from ignition to "ACC" or whatever it's called in Mercedes.

I was wondering for a software solution. There should be an SCN coding or a lower level (trough Vediamo) to change this signal on software level.

PS: Back to hardware option maybe someone has done this before and I assume there could be jumper to switch these signals.

Plato

I have found that rear SAM has two relays supplying power to these two sockets. Any idea how to "natively" change control signal for these two relays so they would activate when key is in 1st position not when ignition is on?

lkchris

First of all, you may know that the W221 electrical system is a CAN Bus. This means it's a computer network and various components receive power per the programming. These sockets, for example will lose power after a certain period of time when ignition is switched off to prevent draining battery. Leave a door open and interior lights will eventually extinguish in same fashion. Have taillight unit bulb fail, and system will substitute another bulb for that function. Obviously, power to these sockets before engine start is seen as another potential battery drain.

The reason for CAN Bus is to minimize the amount of wiring per German regulations regarding managing landfills.

My German motorcycle uses a single, single filament bulb for both tail light and brake light. 5 volts for tail light, 12 volts for brake light. One wire eliminated.

Tapping into or changing CAN Bus circuits is questionable. Best bet may be to run wiring direct from the battery.

https://en.wikipedia.org/wiki/CAN_bus