Little Electrical Questions

[dldubois]

I've had a couple of electrical quirks lately and would appreciate any input.

1.  My door indicator light wasn't going off.   Did some searching here and discovered low brake fluid could be the culprit.   That was it.  Problem solved.

2.  I noticed that if I open the door (w/out a key in the ignition) I can hear the electric fuel pump?  Is this common and I just never noticed it before?  If I close the door its gone.  The sound returns when the key is turned in the ignition.

3.  I've noticed suddenly that none of my dash lights come on.   I'll turn my headlights on but have no dash lights.  I know the control for these lights is located in the bottom of the center cluster and that has been turned this way and that (what little it turns) and still no lights.

Any thoughts appreciated.   Thanks much.  The weather's great now and I'd like to know how fast I'm going as travel the neighborhood at night.  I also miss my colorful heater lever lights.....



Dana DuBois

1970 280sl White (050)4spd
Corinth, TX

[ja17]

Hello Dana,
Adding brake fluid should solve the "fuel pump on" sitiuation also. Power bleeds back through the door ajar circuit .

The rheostat switch on the instrument cluster has a coil which corrodes from lack of use, and looses contact. If you move it back and fourth numerous times it will usually  clean itself up enough to start working again. Also check all the cars fuses they will also loose contact from tarnish or corrosion and will loose contact even though they look good. Twisting them back and fourth will also restore the continuity.

Joe Alexander
Blacklick, Ohio

[hands_aus]

Here is a copy of a file from the internet about your door ajar light and the fuel pump. Obviously this is a "borrowed" document and credit must be given to the person mentioned.

What's the Deal on the Brake Warning/ Door Ajar Light?
By Ola Kristofersson
When you open the door on a 113-model car, the red brake warning light 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.



Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[dldubois]

Much of this has been solved.   I guess I've never had my brake fluid get low before.  Thanks much for the input.  

All issues were related.  I added brake fluid and all was solved.  Even got those dash lights back.