A lot of washer pumps require they be lower than the level of the washer fluid. I am unsure if that's the case with this one or not, but that's why they're often built into the reservoir. If reversing polarity doesn't correct, you may need to see if submersing it does. Also: There are check valves in the original lid you appear to be using, how do you have this setup? I see you have 2 lines still, this mod should allow you to run just 1 line from the reservoir (to the pump, then to the cowl squirter)

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Back in the saddle - 1972 280SE 4.5