Reserve fuel light - TEST

[Benz280]

Looking to identify a way to test the reserve fuel RED light.
Obvious way would be to drive until light turns on, its also a good test of walking to your nearest gas station if its not working.
   

[BobH]

Hello, if you take the cover off the connector to the fuel sender in the boot/trunk, you can simulate the fuel sender contacts, there's no need to pull the plug from the sender

Bridge the earth pin on the plug to the other two pins, ground to the blue black wire should activate the gauge, and ground to blue green wire should illuminate the low fuel light, do these tests with the ignition on

[Cees Klumper]

I did this test the other day. With the fuel gauge on the 'E' mark, where in my 20+ years of ownership I always decided better fill up but then was always wondering why I could only fit about 60 liters in rather than towards the 80 that a 280 SL is supposed to be able to take, I decided to siphon out all the remaining fuel in the tank. Indeed another 20 or so liters came out and, for the first time in my ownership history, the little warning light came on!
So I finally settled that the fuel gauge is essentially way too pessimistic and when the needle is that low, there's still around 20 liters available and I only need worry when the light comes on.

Of course, BobH's method is much, much easier!

Carrying a little 5 liter reserve tank in the boot can be a good idea, just in case that next station is too far for comfort.

[BobH]

Linking wires across the plug will prove the gauge, wiring and lamp, but doesn't prove the sender is ok, only Cees's method, or removing the sender and manually moving the float in different positions will prove everything is working

[Benz Dr.]

Light on should be in the 5 to 8 liters range - not 20 liters.

[yves]

I did the test some months ago and the light switched with 5 liters remaining

[rwmastel]

There's a short fuel pump and a short water pump.  Maybe Cees found a short (improper) sender unit?

[Benz280]

Thanks all, light works .
I still believe that having a 1/2 a tank is the best piece of mind.