What is the "thrid" line from the windshield washer lines
 

I';ve searched, but this is darn arcane.

Finally putting back the washer tank reservoir after monkeying with the engine and one of the washer lines ( I believe the windshield one as opposed to the headlight one), has a little pigtail of a , I donnow, ambient temp sensor on it> simply a wire, few inches long covered in black rubber. The rest of the line clearly plugs into the pump.

I have no clue as to what this thing is and didnt notice it being plugged in anywhere when I removed the reservior.

THis is a heated reservoir, ala 1995.

What in tarnation is it???

THNX., yet again!

connector for a second pump?

Nope. The system has two pumps, two lines, the lower line has this 2" pigtail" off it, with a rubber end.

Enigmatic cars, arent they?

Vent?

controls heated lines
 

My '92 300SE has the same thing, and I'm pretty sure it's part of the circuit that controls the heating of the washer fluid lines. Mine looks like a thermister (resistive device used to measure temperature), but I could be wrong.

I know it's attached to a wire that runs inside the hose that goes from the pump to the windshield nozzles. It would be logical to provide heat to that circuit by warming the wire by applying voltage to the circuit in which the wire is the resistor. Kinda like a really small stove electric element.

Just my 2 cents.

pretty valuable 2 cents. Guess I'll find out sicne now, for some reason, the main washer pump doesnt actuate. I have the headlamp washer wires hooked up there now. The schematic will tell all!

And a 'bump' to this thread...

I was investigating a leaky washer pump on my 89 300E - and found that the 'whatever it is' on the end of the hose was only connected by one wire. I removed it, and I'm trying to make sense of whatever is in it.

I probably will strip back the original hose to expose more wire, spice in some plain hose to connect to the pump and the 'whatever it is' on the end of the wire. [If it's a diode there may be some polarity issues...]

It's a diode
 

I looked at the schematic [page 186 of the PDF, labeled page '160' in image/table of contents]

A diode is indicated at the end of 'R2/7 Heated Windshield Washer Pump Hose'. Now I need to figure out the polarity on the hose itself [only one wire is indicated as the heating element.]