page 16 is showing a single relay, and one inline fuse.
would say check the relay and inline fuse.
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testing controller....
unplug the chassis cable between plow and vehicle. and plug in controller.
you should be able to press a button on controller, and at same time run a multi meter across the pins at the vehicle chassis cable end. to see what you get if anything as far as dc 12 volts.
page 16, pin 1 = black. = neg cable on battery. all others = positive, if i am reading schematic correctly.
exception the black/yellow = lights.