Windshield washer system, wasn't standandard equipment, until 1966 on trucks, so it is hard to say what equipment your truck has and what may be causing the low fluid pressure. The pump is typically mounted on the wiper motor & is activated, when the wipers are switched on. The wiper motor has a cam on the drive shaft, that activates the pump. A number of things can cause little or no fluid pressure, including low fluid level, missing or dislodged pick-up tube in the reservoir, compromised fluid lines, faulty diaphram in the pump or lower motor rpm's. take a closer look at the system and the components, lines & wiring, to be sure everything is in good working order
