Dose not work rigt side rear turn signal - 2009 Mercedes-Benz ML 320

I saw this question after answering your other question. Where you didn't say rear left, but only left side not working. You can forget my other answer, if your front left signal stays on bright without blinking, when you signal for left turn. If that is what is happening, the problem could be the socket for that left turn bulb. Do you see any rust or corrosion in the socket when you pull the bulb out? Do you see any broken or stretched wires at the light assembly or going to that assembly? A voltmeter would be your best tool to look for power inside the socket when key is on and left turn is signaled. You also need to remember that that socket has to have a ground wire too. And when a bulb won't light, you need to check both for power to the bulb, and for the ground leaving the bulb. The ground has to be good-it can also be tested with a voltmeter. Even a $5 test light is good for checking for power. Easy to learn basics, too. If you have to do your own work, you might as well get good at it.

In the diagram for rear lamp, the top wires are voltage, the bottom black wire is ground. The brown wire on either side should be tail lamps, goes hot when you turn on the headlamp switch. The other top wire on either should be for turn signal. With everything turned on, is there voltage on that wire?
Because the front works and the rear don't, possible wiring circuit problem? The voltage for turn signals comes from bcm. The bcm knows when you turn on turn signal switch, either side, then the bcm sends voltage to turn signal lamp at the rear and front.

it could be a bad signal flasher . are the signal lights all working at both ends of the car.

Has the vehicle been in an accident on the left rear side. First check the bulb to be sure it is not defective, trade it out with the side that works properly to test. If the bulb works well then My thought are you may have a shorted wire. The turn signal flasher works by heat build up within the flasher the heat is caused by the load of the bulbs, the load heats the metal spring causing it to open the circuit then as quickly as it cools down the circuit closes again lighting the bulbs.
There is also a possibility of a defect in the turn signal mechanism on the steering column. The turn signal switch on many models does three different things on many models that use the same bulb element / or bulb for brake and turn on rear of vehicle. It controls the circuit for brake light by sending power both left and right side rear when turn signal is in neutral position then when turn signal is in left turn the switch cancels brake light power to left side rear and supplies flasher power to left side while maintaining brake light supply to the right side rear, and so on opposite when the right turn is chosen on turn signal switch. The turn signal indicators on the dash normally run off the same circuit as front turn signal bulb only which is also controlled by turn signal switch. Front has turn signals but no brake light.
I think there is an additional load on the left side rear turn circuit and it could be either a wire that is shorted or the turn signal switch if the same bulb element is used for both functions.
Often times if trailer lighting is connected the flasher will also blink a little faster because of the extra load of additional bulbs.

Front right and rear right are on a different circuit than the left front an left rear. Locate the Flasher control module behind dash. With key in RUN position check for pulsing battery voltage on the Green/white wire coming out of the flasher control module electrical connector. If no battery voltage, check for battery voltage coming into the flasher from the turn signal switch on the white/red wire. Left turn input is on the white/black wire. If not battery voltage on white/red, but voltage on white/black when turning left, then the turn signal switch is bad

remove rear left lens and install new turn signal bulb.

check the bulb there some bulbs have two elements in them the turn signal element might be broken change the bulb

that is a classic symptom of a bad flasher.

Have you checked the breaklight switch under the dash? It works off the break peddel arm it could be bad or out of ajustment.

SOUNDS LIKE BROKEN WIRE IN DOOR JAMB