On my '84 300D euro, I have a warning light on my IP that lights up when I step on the brakes, so I assume it's a brake warning light. However, there's already a red brake warning light right next to it which does not light up. This particular light is yellow, and it has a circle symbol with dashed arcs surrounding it on either side. Is this also a brake light? Perhaps for low fluid, air in the lines, or worn pads?

By the way, I would consult the owner's manual, but I cannot read German...