Usually it wont work until the truck has built up air pressure just like the wipers, horn, etc... There is a valve that makes the brake system a priority and will only give air pressure to the accesories once all the tanks are full. Thats how mine is. If it happens on and off even with air pressure to the accesories then i dont know the problem.
I thought that the 800's windshield washers were just a simple pump you actuated with the windshield washer lever.
If that's the case, I'm sure you can disassemble the pump and replace the o-rings. Should work good as new again after that. I'm sure the o-rings just dry out due to the alcohol contained in windshield washer fluid.
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