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1976 240D 115 Pumpkin Orange 700,000+ miles and rising!
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Discussion Starter #1 (Edited)
I have decided to phase out the foot pump for the window washer fluid (yes currently working) with an electric pump.

I thought I could do it simply by running power off the current foot pump switch to the pump and then when the foot pump is pressed I thought it would turn on the new electric pump. When I do this all it does is complete the circuit and the washer blades run all the time but not pump. I know the pump works (directly to battery water shoots out) but piggy backing on the foot pump does not.

Next I run lines from the foot pump switch into my own 12v switch and then to the new pump. Now as expected the power does not just continually run to the blades (when new switch is off). When I turn new switch on the blades come on as expected and wanted but still the pump does not. Still just seems like it is completely the circuit for the blades but does not activate the pump.

What am I missing - this should work. If it wont work anyone have a suggestion on knowing what cables are what to be able to splice into for the power? How do you tell whats what up under there?

I know this is confusing to read but long story short:

If I try into the power on the foot pump no matter what I do it completes the circuit for the blades and turns them on but will not turn on the pump too.

Thanks!

EDIT For Pic
I have all that and i know I can do it from another power source - I am trying to piggy back it off the existing switch "for the heck of it" and to have it also activate the wipers at the same time. Granted doing another switch in same spot will still do this if both switches are depressed (current and new) but would be nice to have just one. I have updated the original post with a pic of the most basic wiring I could think of as a test and still doesnt work.

The connector to the foot pump switch i have tested with multimeter and it is for sure 12v and i know which is +/-. When I test this it completes the circuit and the wipers turn on. So as you can see in the original pic I tried directly wiring the pump into the connector (purely as a test mind you) and when I do this the blades activate but the pump never turns on. I did this test just to make sure its not a switch or splice problem in my other tests. Should this not work and activate the pump as well?
 

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73 280SE 4.5, 71 300SEL, 03 BMW Z4, 72 Fiat 850, 80 Triumph TR7, 85 Porsche 911
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Easy fix :) Take out the assembly and get rid of the water bulb. At any hardware store (Lowes, Home Depot, Ace Hardware) buy a large on/off button. It should be the type that pressing it closes two contacts, and little else. Run one of the leads to a power source and the other to the pump. The remaining lead from the pump will be attached to ground (any local screw to attach it to the chassis will do).

I did this and used a piece of wood to mount the button to the whole assembly. When I hit the foot pedal, the button actuates and causes the pump to run, as well as causing the wipers to move.

In all, it took me about two hours to do...
 

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1976 240D 115 Pumpkin Orange 700,000+ miles and rising!
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49 Posts
Discussion Starter #4 (Edited)
Easy fix :) Take out the assembly and get rid of the water bulb. At any hardware store (Lowes, Home Depot, Ace Hardware) buy a large on/off button. It should be the type that pressing it closes two contacts, and little else. Run one of the leads to a power source and the other to the pump. The remaining lead from the pump will be attached to ground (any local screw to attach it to the chassis will do).

I did this and used a piece of wood to mount the button to the whole assembly. When I hit the foot pedal, the button actuates and causes the pump to run, as well as causing the wipers to move.

In all, it took me about two hours to do...
I have all that and i know I can do it from another power source - I am trying to piggy back it off the existing switch "for the heck of it" and to have it also activate the wipers at the same time. Granted doing another switch in same spot will still do this if both switches are depressed (current and new) but would be nice to have just one. I have updated the original post with a pic of the most basic wiring I could think of as a test and still doesnt work.

The connector to the foot pump switch i have tested with multimeter and it is for sure 12v and i know which is +/-. When I test this it completes the circuit and the wipers turn on. So as you can see in the original pic I tried directly wiring the pump into the connector (purely as a test mind you) and when I do this the blades activate but the pump never turns on. I did this test just to make sure its not a switch or splice problem in my other tests. Should this not work and activate the pump as well?

If I can not go this route - what is the easiest way to figure out which wire up there I can splice into for power?
 

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1976 240D 115 Pumpkin Orange 700,000+ miles and rising!
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Discussion Starter #5
Thanks Grubeguy your response gave me what i needed to at least figure it out - i wasnt passing one through and one to ground was passing them both through. I did just do basically what you did - took a piece of wood sunk a momentary open switch into it passed the pump wire into it and pulled one out of it to the ground and have the pump wired to power and replaced the rubber bulb with it all is working well now. One question - the first spout has so much pressure it basically shoots over the car and the second one in line barely has any so it trickles out. Any suggestion on how to compensate for this? I have single spray hole spouts FYI.

Thanks again!
 

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73 280SE 4.5, 71 300SEL, 03 BMW Z4, 72 Fiat 850, 80 Triumph TR7, 85 Porsche 911
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The first spout has so much pressure it basically shoots over the car and the second one in line barely has any so it trickles out. Any suggestion on how to compensate for this? I have single spray hole spouts FYI.
Glad I could help! Those nozzles are adjustable. Take a needle, push it in the opening of the misbehaving one, and adjust as necessary. When I first rigged mine up, I had enough pressure to shoot well over the trunk :)

I had given some thought to rigging up water outlets directly on the wiper blades, but I'd need to do some minor plumbing work and drill holes. Still, not without the realm of possible, eh?
 
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