It is the sea switch or the wires between the seat switch & the brake switch.
Try turning the blades on & off while sitting on the seat, engine off.
You should hear the clutch going KLUNK if not then that confirms the seat switch / seat switch wiring is at fault .
Wiring includes relays were fitted but we can not check for them unless we have the full model & serial numbers from the tag under or behind the seat so we cal look up the correct wiring diagram.