Congatulations on the 4560 purchase. They are a great tractor. If you are lucky, the pressure sensor is bad or a wire is shorted out. If you are not so lucky, the pressure is actually low. Low pressure can be caused by a worn transmission pump, a leak in a clutch pack in the transmission, a blown gasket somewhere, or a weak spring in the pressure regulating valve. When the light is on, is it on constantly? Try shifting through all the gears and see if the light is only on in certain gears. Try turning the pto on and off to see if it has any effect on light. When you shift through the gears, apply the brakes to put a load on the engine. See if the transmission slips in any of the gears when you push on the brakes. If the trans slips in certain gears, post back here which ones and I can narrow down possible problems. If there is no slippage and everything seems to operate Ok, chances are the sensor is bad. It is part number RE25658 and is item number 6 in diagram. It is located on clutch valve under the left battery.