heater fan runs when driver's door opened, key in hand

[pauloe]

Today I opened the driver's door and the heater fan came on high speed (fan switch was set to high).  This is all before I had put key in ignition.  With door still open, I could control the fan speed with the fan switch, including turning it off.  If I closed the door then fan always off.  Open door again and fan came on (controlled by fan switch).  Then I took car for a drive.  After drive, car well warmed up, this funny behavior was now gone.  Will try again in morning when car is cold.  Any thoughts?

[Pinder]

Ive encountered some strange issues if the brake fluid level is low and the door is open.

https://www.sl113.org/forums/index.php?topic=20425.msg144694#msg144694

[Pinder]

in my case , I was also unable to shut off the engine if I had the door open.

[pauloe]

Pinder yes.  I also had to top up the brake fluid reservoir today because light was on.  This was between the time it was acting funny and later
when it was ok.

I topped of the brake fluid reservoir while the engine was warming up, so I missed getting a data point on your observation of being unable to shut off the engine.

I will see how it looks tomorrow.
Paul

[rwmastel]

You could remove some fluid for testing, if you're that curious.

[pauloe]

It seems this glitch is a feature that can be fixed by adding a diode.  This jives with Pinder's observation that engine keeps running when door open and you turn ignition switch off.  Closing door would then stop the engine.

following is from: https://www.peachparts.com/shopforum/vintage-mercedes-forum/221611-280sl-1968-brake-warning-light.html

05-08-2008  Arthur Dalton

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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[Pawel66]

pauloe, Pinder,

It is a known topic, described on the Forum many times.

As in the US they started to require cars to have the "open driver's door" warning light indicator in the dash, folks at Daimler had to figure out how/where to place this warning light and how to hook it. Due to lack of space or better idea and to make it in a simple and cost effective way, they hooked the brakes fluid level control lamp in instrument cluster to door switch. This control lamp, however, was already hooked to the low fluid level switch in brakes fluid reservoir.

Since the door switch is under power at all times and brakes fluid level indicator is under power after ignition, a connection of two universes happened here - one with power at all times, one with power after ignition.

What happens if you open the door when your brakes fluid level is low and its switch is closed: power goes from door switch, to control lamp in the dash where it meets wire from brakes fluid level switch, then goes to this switch and if this switch is closed, goes to fuse no. 5. Fuse no. 5 is normally under power after ignition - together with fuses 2, 3, 4 and 6. All those fuses get power when you open the door. Anything that is connected to them will switch on if it is switched on. The most commonly noticed is fuel pump. 

When the brakes fluid level is above minimum, all the above does not happen because power will not go through switch in brakes fluid level reservoir. You can unscrew the brakes fluid reservoir cap (any of them) and lift the float - the switch will close and you can see or hear devices switching on in the car.

[Pinder]

Yes thanks Pawel; good description. I first came across this when I was working on my car several years ago bleeding the brakes, and at first I thought the car had a resident ghost playing tricks on me. I then read up on this strange behaviour on this site. I think its an interesting "feature". I wouldnt want to correct it in anyway; just keep the brake fluid topped up.

Regards

 Pinder