1970 GMC C20 Washer spray pulse with wipers
 

I'm working on restoring a GMC C20 and I can't figure out the issue with the washer. The washer functions normally when the switch is turned to the spray position but when the just the wipers are on low or high, the washer sprays each time the wipers start to move up. All the parts are brand new (switch, wiper motor, and washer motor). I though it might be a ground issue so I ran a ground wire to the mounting screw that grounds it but it still doesn't work correctly. I tried the old switch (and checked the new one) and both only applyou voltage when the spray position is selected. I can even unplug the washer moto but it still spray pulses with each start of the wipers (this continues so long as the wipers are on). This is a 3 wire wiper motor as well. Has anyone seen this issue before or have any idea what might be causing it?