Remove all field wiring from the panel box along with any other option modules that may be attached, leaving only the AC connected to the panel.
Track the circuit that is bringing in the ground fault by plugging each circuit back in one at a time until you locate the fault.
Check the faulty circuit for the wires that are making electrical contact with something other than it should. Look for wires that have been stripped of their insulation, or moisture or water.
Check the panel with all circuits off except AC to see if the ground fault is still present. If so, replace or repair the panel.
Check the circuit wires at all devices along the circuit to make certain the wires are properly installed.
Remove the circuit wires from the panel. Return the end-of-line resistor to the terminal block. If this clears the alarm, the problem exists out on the circuit somewhere. Inspect the circuit beginning with the first installed device.
Check for wire breaks, missing or wrong end-of-line resistors, or too many broken strands on the wire.
Reinstall the field wiring, place the proper end-of-line resistors on the zone terminals of the panel and reset.
Swap the field wiring end-of-line resistors at the control panel to test an abnormal reading. If the problem moves to a zone that has been tested as normal, the problem exists on the circuit field wiring. If the problem remains in what had been the abnormal zone, the control panel may be at fault.
Shut down power completely, if the alarm does not clear. Remove all field wiring, place the end-of-line resistors on all zones, and retest. If problem remains, repair or replace the control panel.