You dont need that relay between the fpdm and the fore relay.
As stated by Malcolm, use 3/10 to trigger the primary pump. The ground is actually the line that switches and that's why you cant use any other ground.
I also used 10 on the positive side of the second pump and used the Hobbs switch to provide ground to lose the circuit. This served two purposes: the pump can only have power if the pcm is attempting to run the pumps, didnt have a hot wire ru nning up to the Hobbs switch.
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Thanks...I really like the idea of running Hobbs as ground to trigger 2nd pump