My car 2013 E350 4matic had warning "Check right low beam" since maybe 3 months ago but the light still on but dim not as bright as the other side. The problem on car inspection it failed because that warning and it is not as bright as the other side. I did convert from Halogen to LED since two years ago. So even one side dim it still visually bright because LED is at least 4 times brighter than Halogen. I checked with voltmeter I got 13.5v same as the other side. I swapped the bulb and the right low beam dim and not as bright as the left side. I did swap the halogen back but still it had warning check right low beam. Attached result from Xentry Diagnostic using Vcxdiag. I think there is problem with ground cable. If I can not resolve I am thinking adding relay to use current circuit to drive relay so the bad connection will not cause drop in voltage to trigger SAM module.

 

You checked voltage I assumed at the H7 bulb connector, it was 13.5V at the right headlight being under load with low beam ON or no load aka OFF ?
Voltage drop test must be done with LOAD.

Since you have Xentry, I suppose you have EPC/WIS to access wiring diagram, why don't you attach it here. Just make sure it is the one for your headlight system, there are a few
variant.

If your High Beam on the right side headlight is not DIM like the Low beam of right side headlight, your issue is not likely the ground cable if the ground wiring are combined between high and low beam. Need wiring diagram to see if the grounds are indeed spliced/shared at some point before the final single ground wire lug to engine bay area.

Is this your car headlight version ? , below :

There is no point of modifying you standard headlight to use relay, it will be easier to trace and make sure all OE wirings are having good contact and no corossion.
I use relay in the old days when using 90/100 watt H4 bulb in lieu of standard 50/55 H4.

Direct from battery : Load test with a stand alone 4 amps load ( H7 55 watts is 4 amps ) both positive and negative cables for the right side low beam with voltmeter reading too.
There then it will show if the positive or negative wire or both are the culprit

Don't forget to make sure the headlight connector female pin has good friction fit to the H7 bulb male pins.
Take a peek if the wire crimp at the H7 connector terminal has kinda melted

My friends 2010 C200 W204 has both its 5 watts T10 front parking light which MB uses as daylight driving light, melted its connector and also the wires.
Always in traffic jam with engine bay ambient temperature at near 90C and those baby 5 watts T10 bulbs itself at 178C easy, the typical automotive wire which at best a 105C rated,
simply can not take such abuse. https://mbworld.org/forums/e-class-w...ml#post8474081

Good luck....

 

Thank you for responding. The picture you attached exactly like I had. I did try to find the wiring diagram in WIS but no luck it difficult to find anything in WIS. This is my VIN WDDHF8JB5DA669595 if anyone can find wiring diagrams I will appreciate. I will try to check I just bought AmazonSmile: ANCEL PB100 Automotive Power Circuit Probe Tester, 12V 24V Car Test Light Electrical Diagnostic Tool Master Kit AC DC Digital Voltage Short Finder, Relay Fuse Tester Trailer 3 System Thermometer 4 : Automotive. I hope I can find the culprit but I may have to open front right headlight. I will do test load but using halogen will be difficult because the connection surrounded by clip ring. But if I use LED it will be easy to tap connection to pos and neg. Now I try to find wiring diagram so it much easier if I know where it go to front SAM module.
I realized I make dumb mistake. Actually I work on high beam not low beam because the position from back low beam is higher than high beam. So the low beam is at the end and when I replace with good bulb no more "Check right low beam". Problem solved by replacing bad H7 led.

 

 

Thank you for schematic and diagram