In my 1973 220D and many other models of similar vintage the windshield washer is operated by a foot pump. This foot pump has two functions - to spray the water and to turn on the wipers.
They have a rubber bladder or ball to push the washer fluid up to the nozzles on the hood and this will fail at some point. When it fails the washer fluid will drip or gush down onto your foot and of course the washer will not work any more.
You can replace the foot pedal assembly (this contains the bladder) if you can find one - but there are all going to be almost as old as yours. I know of no place that is remanufacturing these parts.
The wipers are controlled by an electrical switch also in the foot pedal and these seem to last much longer. So we can modify the system to run an electric pump to pump the fluid powered off of the switch in the foot pedal. This will restore original functionality and in some ways be even better.
The things you'll need are:
- a 12v pump for the window washing fluid. Most any one will do there are generic ones for a few $$ or you can buy one from a newer MB and it will have that star on it.
- a Diode at least 15v and 20a - bigger is fine. These will cost around $1 at any decent electronic store.
- a few inches of heavy gage wire, a bit of electrical tape, solder and a soldering iron
- several feet of tubing (why not replace all of that 40 years stuff under your hood).
- (optional but recommended) 2 new jets - they are also quite inexpensive and if you washer has been non functioning for a while your jets are probably hopelessly clogged.
And a word of caution:
- You will be turning on the windshield wipers perhaps several times before you are done. Make sure the windshield is clean and the wipers are wet so you don't scratch the window.
- You will be opening the hood - it you pull the the windshield wipers up off the windshield remember not to open the hood until you put them back down
- You will be connecting electrical wires make sure that all wires are insulated, connections are secure and that nothing can short out.
Is there water in your system? We will want to drain it - follow the hose from your reservoir, it will go to a 3 hose valve. One is the line you were following, another goes up to the jets on the hood and the third goes down and inside the car - this one goes to your foot pump. Disconnect all of these and pump the foot pump. There can still be some water in it but most it out.
Find the foot pump - notice on the left side an electrical plug. Remove this plug (I do not remember if I had to remove the foot pump to get this off).
On my car the foot pump only has 2 pins - some have 4 and I can't tell you which specific pin you want but it should be easy to figure out. Take your volt meter and hook it to a good ground - now turn the key on (don't start the car) and notice one of the holes in the plug is +12v. Note that on the plug (we want the other wire). Now turn the key off and you should notice that there is no voltage in either side of the connector.
Open the plug - look at the two wires there note which goes to which hole in the plug also the orientation of the plug because you will want to get it back together the same way. Now cut the second wire, the one that was not +12v and insert the diode, solder. Add a second wire 4' should be fine and this wire does not need to be as heavy gage - solder this to the plug side of the diode.
NOTE you must put the diode in the right way - that is the cathode (the end with the stripe - if yours has a stripe) goes toward the wire and away from the plug / foot pump. Otherwise your window washer will spray whenever you turn your wipers on.
Insulate the connections, reassemble the plug and re-connect it to the foot pump.
This is a good point to test - turn the key on. You have the 4' of wire that you just connected to the foot pump (this will be power for the washer pump) connect it to your volt meter (the other side ot the volt meter is grounded) and there should be no voltage. Turn on the wipers (from the switch not the foot pump) and there should still be no voltage. Turn off the wipers and step on the foot pump - the wipers should come on and now you should see 12v on this wire. IF NOT go back and fix it - there is no point to continue.
Once you pass the above test turn the key off - find a hole to shove that wire into the engine compartment (probably the same one the hose that went to foot pump) and shove all of the wire through it. No slack on the inside.
The rest is fairly easy - find a suitable spot to mount your pump. secure it and run new hoses to it. Run the power (the wire from inside) to it and a ground.
Changing the jets is done by squeezing the bottoms (under the hood) of the old ones and pushing them up. Put the new one in and hook up the hoses.
You should be in business. I will add some photos.