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Old 05-07-2008, 09:15 PM
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Join Date: May 2008
Posts: 3
280sl - 1968 - Brake Warning Light

Red indicator light on dash panel stays on.
Manual states this is a low brake fluid light.
Checked brake fluid - full
Tested wires - all connected and have juice
Checked fuse #5 - replaced - light still on
Checked fuse #1 - removed and light goes off.
Emergency brake not engaged

What's next?

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Old 05-07-2008, 11:10 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,804
Brake indicator lamp will also go on if door is ajar.
When Benz added this feature ,[ early 113 did not have reservoir level monitoring lamp] , they mistakenly had a wiring glitch in the added circuit, but here is the fix.

<< By Ola Kristofersson
When you open the door on a W113-type car, the red brake warning light in the central kombi instrument cluster comes on. This is to signify that the electrical brake warning system is working OK. So why is the red brake light associated with opening the door?

Legislation demanded brake fluid low and door ajar warnings. There was only one light position left on the kombi instrument, so they decided to use the same light for both functions.

First, a description of this W113 feature:
All Mercedes cars are designed so that when the key is switched to "on", the wiring section No 54 in electrical system is in use. Section No 30 is straight from 12V+ on battery. A primary rule is that section No 30 and No 54 are never to be connected, as this bypasses the ignition key and empties the battery.

The 113 is designed so that:
The courtesy light below the dash is connected to No 30. Light is (may be) lit as door is opened. Brake fluid warning is connected to 54 (Light is on when car is running and level is low). Now, the M-B designers wanted to find a way to check that the warning light bulb was OK. And, they did that by using the courtesy light door switch. This also resulted in a "door ajar" warning function.

This design carries with it an unfortunate effect: If the brake fluid level is low, and the door is opened, 30 and 54 will be connected. Means ignition will go on, and the fuel feed pump will start up. Fuel can be squirted around if one is performing work on the fuel system in the car. A wise thing to do is to disconnect the battery before starting any maintenance work on the fuel system.

Now, a remedy:
By simply fitting a diode in the circuit between the fluid level sender and this red light bulb in the combi instrument. A Si diode, 1A with the (+) side facing the bulb will do fine, and it may be easily hidden in the wiring harness of the car.>>>>>

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