And a self-inflicted one at that! :Thumbsup:
Having installed an M bumper recently that had the cut outs for headlight washers, I decided to proactively add the functionality to my car so as to, hopefully, pass MOTs with my aftermarket HIDs intact.

I took the car for a pre-emptive MOT last week and sure enough it only failed on the headlight washers (present, therefore must work). He commented that with Xenons, the washers need to work.
So, the install I have done is with the correct reservoir, pump and pipe work. I’ve spliced into the wiring for the windscreen washer pump so that both activate at the same time.
However, when I operate both at the same time, the pumps fire up and then lose pressure – then cut out. (Pressure drops within about 1.5 seconds then the pumps cease after about 5 seconds). The windscreen gets the most water and headlights may or may not get any randomly!
Tests I’ve tried:
- Headlight washers on their own. OK
- Windscreen washers on their own. OK
- Together with Reservoir open. FAIL.
- Together with reservoir closed. FAIL.
The only thing unusual about my setup is the lack of the correct relay and the lack of an independent power supply. Please correct me if I’m wrong, but I can’t imagine a shared power supply would be supplying inadequate power? Devices draw what they need to draw as I understand it (or it would blow the wiring or fuse).
Therefore, I’m left to wonder whether the relay does some clever pulsing that prevents some pressure issue OR one of my pumps is actually working below strength – though I’m not sure why the latter would cause problems when they work independently.
I’m so, so stumped.
I obviously have the fall back of returning all to normal to pass MOT each year, but that’s far from ideal and a bloody big disappointment!
Has anyone else done this conversion and can confirm it works or resolved similar issues?
Having installed an M bumper recently that had the cut outs for headlight washers, I decided to proactively add the functionality to my car so as to, hopefully, pass MOTs with my aftermarket HIDs intact.

I took the car for a pre-emptive MOT last week and sure enough it only failed on the headlight washers (present, therefore must work). He commented that with Xenons, the washers need to work.
So, the install I have done is with the correct reservoir, pump and pipe work. I’ve spliced into the wiring for the windscreen washer pump so that both activate at the same time.
However, when I operate both at the same time, the pumps fire up and then lose pressure – then cut out. (Pressure drops within about 1.5 seconds then the pumps cease after about 5 seconds). The windscreen gets the most water and headlights may or may not get any randomly!
Tests I’ve tried:
- Headlight washers on their own. OK
- Windscreen washers on their own. OK
- Together with Reservoir open. FAIL.
- Together with reservoir closed. FAIL.
The only thing unusual about my setup is the lack of the correct relay and the lack of an independent power supply. Please correct me if I’m wrong, but I can’t imagine a shared power supply would be supplying inadequate power? Devices draw what they need to draw as I understand it (or it would blow the wiring or fuse).
Therefore, I’m left to wonder whether the relay does some clever pulsing that prevents some pressure issue OR one of my pumps is actually working below strength – though I’m not sure why the latter would cause problems when they work independently.
I’m so, so stumped.
I obviously have the fall back of returning all to normal to pass MOT each year, but that’s far from ideal and a bloody big disappointment!
Has anyone else done this conversion and can confirm it works or resolved similar issues?