Low oil light is always on.
 

I changed the starter in my 87 420 the other day and now the low oil idiot light is always on. The oil level is at the proper mark.

How does the oil level sensor in these engines work. What is the basic detection mechanism?? I know the sensor is inside the crankcase so its a bear to get to.

Any ideas on what to look for?

Having a 1987 300D as the reference, the low oil light comes on when the lead to the sensor is grounded. The sensor is fit with o-ring into the upper side of the oil pan and has a connector pin for a signal wire. This wire goes into the wiring harness at some point.

Most likely reason for a sudden appearance of the dash light, after working on the car, is a pinched and grounded wire to this sensor in the engine compartment.

Hope this helps,
Ken300D

Thanks Ken. I can imagine what I did but at least I know where to look.