This seemed like a fairly simple issue to me, but...

I want to test the windshield washer fluid level switch from my 86 300SDL. I have the switch out of the tank. It has two connections on top. When you turn it upside down, there is a clunk. I know from disassembling one that there is a float inside. I assumed that when the float drops to the bottom, there should be connectivity across the two connectors at the top, and when the float floated up, the connectivity was broken.

I now have another used switch. Both my disassembled one and my "new" used one never show connectivity, whether right-side up or up-side down.

Do I now have two failed switches? Or do I not understand how these work? Help appreciated.


Just for fun, I have attached a photo of the disassembled switch. From left to right, the parts are 1) bottom plate, 2) fluid drain regulator, 3) float, 4) switch body.

The float has what appears to be a ferrous-magnetic ring at the top which I assume causes the electrical field change necessary to signal low fluid level. The "fluid drain regulator" (my terminology) has a small circuitous channel to slow the fluid drain rate from the switch, much like what you find in the bottom of the fuel sender unit.

Attached Thumbnails

 

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

Good question I'm not certain if its a simple open close contact or other type of sensing unit. When I had replaced mine I believed I checked for open close contacts on the new one and could not see it functioning on the bench but once installed it worked just fine. It's been a number of years and my memory of that event is somewhat sketchy. Perhaps a wiring diagram may shed some light on the subject.

Does anyone know how to test these short of putting it back in the tank, reconnecting the wires, filling the tank and looking at the idiot light?

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

Switch in the air in its normal orientation - continuity, light on.
Switch in the air upside down - no continuity, light off.

These do fail pretty regularly and are not that expensive (~$25). Hella is the OEM manufacturer. I would just get a new one.

Note to all who follow who have a W210: They did a really interesting trick (?) with the coolant and washer tank sensors. Both sensors are wired in series to one analog input point on the front SAM module. There are series and shunt resistors inside each switch. The SAM reads the resistance of the chain of switches and resistors and can determine the various states of the system (i.e. normal, low coolant, low washer, or both). If one of the sensors has failed internally or is disconnected, the resistance value will be wrong and it will show "Display Defective" on the screen. The upshot of this point is that you cannot test a W210 sensor with a meter unless you know what the resistance values (both full and empty) are for a good switch.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

THANK YOU JAY BOB. PEACE & BLESSINGS