The original owner of my w115 did something similar, but instead of a pressure switch, the simply installed a new switch in the center console. So not ideal/original, but my car has always been utilitarian. I still use the foot pump to trigger the wipers and then flip this switch to run the washer fluid.

I had to replace the pump finally and it was interesting trying to buy a replacement. Car parts stores have trouble selling you something if it isn't in their computer associated with your make and model of car. And they didn't have any out for me to just pick one myself. All in all, it is probably a $15 mod.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).