Dashboard Indicator
 

I have a 1985 500SEL with 139K. About 50 miles ago a dash indicator lights intermittently. The manual I have states this is for outside temperature. The indicator is round and amber in color. There are 3 little lines around the left and right sides. Can anyone advise? I disassembled the front brakes and the pads are in good shape. I looked at the sensors, which looked ok. After putting everything back together, the light was out. I do feel the sensors were the problem. Brake dust????

Sounds like the brake pad wear indicator to me.

I agree with Steve, the symbol you describe is an indicator that the front brake pads are in need of attention.