Unfortunately the voltage tester I bought turned out to be AC only. Can someone please confirm for me that the brown wire is ground and the yellow/pink is 12v. Thanks for your help!

 

This is what you want. $3 on Amazon.

 

Does your voltage tester measure resistance?

 

Hard to tell without your specific wiring diagram. Can see from this other photo of a W204 the wire colors are not consistent. I think its safe to assume the brown is ground and the other large wire is 12v. I think the thinner wire is for the lighting.



I was thinking if your meter can test for continuity you should be able to at least check for the ground wire. Connect one probe to something metal attached to the frame then test the wires on the harness from the car, if the meter beeps its ground.