little yellow light at fuel gauge
 

upper left of fuel gauge in an '85 300SD....The tank needle was responding to the addition of fuel but the little yellow light never went out....Any ideas?

Rob M Concord, MA

Most likely it is the sending unit. However, having taken mine apart, it is a bit difficult to explain how the low fuel light circuit could be closed if the float has lifted off the seat (needle is moving toward full). The sending units do get gunked up with diesel over time, and mine needed a good cleaning. This is an easy repair on the 123, but am less sure about the SD. You should be able to do a search on fuel sending unit in the Diesel Discussion and get some help.

The metal piece at the bottom of the float that makes connection to turn on the light may corrode and fall off the float. It would then short out the contacts. These are not too difficult to remove/replace. Bad thing is, on your car I believe you have to remove the back seat to get at the sending unit. Once the seat is removed, job is a breeze.

I noticed that light is on on my MB too.

I honestly thought that it was supposed to be on "all the time" so you can see the fuel gauge needle at night when it passes in front of the light. That way you know you're low on fuel when you can't otherwise see your gauges.

I've grown accustomed to it. That little light is the brightest thing on my dash!

- Patrick