I don't have the GN1 fans but I do have a very similar setup that used the Caspers harness. The only issue I had was it was the connection to the fans themselves came unplugged easily. I ended up completely re-wiring my setup with a MSD solid state relay when I went over to the Holley.
Did you apply 12v directly to one of the fans at a time from the battery to make sure the fans work? If you have voltage going in (fuse link) voltage at the trigger wire (from stock harness) and you verify the fans work it has to be the relays or the wiring for it. I would give Caspers a call to see if they have any troubleshooting advice for it.