1979 Mercedes Benz 450slc Reservoir grommet replacement

Is the parking brake release ?if not release it., or your brake system has a potentially serious hydraulic problem that may make your vehicle unsafe to drive.

The master cylinder reservoir has 2 chambers with 2 sets of electrical contacts. Loss of brake fluid in either reservoir will light the warning light on the dash.
First, check the parking brake lever, handle or pedal. Make sure it is fully released. If that is not the problem, test the brakes by pressing on the brake pedal. If the light comes on only while pressing the pedal, it means one of the hydraulic circuits in the brake system has lost pressure -- probably because of a leak (bad brake hose, leaky disc brake caliper .
Your vehicle may or not be able to stop with this kind of problem, making it unsafe to drive. If the pedal feels unusually low or goes to the floor, DO NOT attempt to drive the vehicle.

That was a nice reply to someone who knows nothing of cars. I explained that I had replaced the grommet seals on the master cylinder reservoir and had the reservoir upside down while performing the repair. Frankly, I expected a more detailed response to my specific problem. This is somewhat disappointing, especially since I paid five bucks and waited a day for the response. Can you do any better?

The arrow indicates the location of the reset pin on a master cylinder equipped with a pressure differential warning valve must be reset . thanks