I've checked the fuses, and tested the low and high beam fuses to see if they're getting any power, and they're not. After looking at a wiring diagram it seems as if the issue has either got to be the headlight switch or the combi switch.

Most everyone with this same issue has had it be the combination switch, though it seems as if the switch gets progressively bad over time, mine just stopped working with no signs of it going bad previously. The switch I did by off ebay is used, but in excellent condition, and I would imagine that since the switch is a mechanical device that when it does go bad it will physically not work to well, both the one in my car and the one I purchased still physically work well, they're very tight and not loost at all.

It seems that buying a new combi switch is the way to go, though what I'm worried about is that after I buy this switch it still might not solve to problem. Then I'll know for sure that it's not the combi switch but something else which, I, or anyone else as of yet seems to know what it might be. I have a strong feeling its something else, maybe the headlight switch, but everything else (parking and fog lights) work. I'm trying to avoid spending a fair amount of money on parts that I can't return to not know for sure if it will solve the problem.

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1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500