Oh. So it’s just that Mercedes decided that they wanted to be patching 12V around instead of patching ground around. Gotcha. So basically the two connectors need to have nothing to do with ground otherwise we sink our 12V when button is pressed.

So if this new horn button’s two contacts don’t beep out to gnd on the continuity checker, then I suppose this horn button will wire up fine with a Mercedes. I guess I’ll do a check for this. But maybe back in the w123 wheel connections there is a third ground wire I can just omit from the new button or something.