General Pump ZK1 Unloader

Ok. My Pulsar 280 unloader just died. It will no longer bypass when the trigger is released and it’s putting the engine under a load and spiking the pressure on my pump. I have disassembled it and found no obstructions and/or damaged check balls or springs. It may just be worn out. I really don’t know (over 500 hours and 2 years worth of ownership). After reassembly, it still will not work. I have been reading every post I could find on unloaders from 3 different BBS sites and really haven’t found much on this particular unloader from GP. I’m replacing the 280 with a ZK-1. My machine is rated for 3500PSI so I didn’t go the K7 route. Anyone with experience on these unloaders? Can I use the pressure gauge on the pump at the discharge outlet to set pressure or do I need to tap into a port on the unloader itself? Will my current pressure switch work correctly with this type of unloader or will I need to change something. Will it plumb the same as the 280? I have a Delco RK-41XP with the bypass currently plumbed with a 3/8 hose into my tank.

A pressure switch senses pressure and cuts the fuel when there is no pressure. It should be installed on the pump for best results. On the port on the top left or right of the head. Usually 3/8 pipe thread.
An Unloader is a wear item and they have been known to go bad prematurely if you starve your pump of water. I suggest you check out the valves in the head as well.