Abstract: An interlock system for a lawn and garden tractor or similar vehicle includes a PTO switch having off, on and momentary on positions and connected to a latching relay to provide PTO operation in reverse if the switch is moved to the momentary on position prior to the vehicle being shifted into reverse. Once the vehicle is operating in reverse with the PTO activated, the operator can release the switch from the momentary on position and the PTO will remain activated. However, once PTO operation has been interrupted for any reason, the PTO can be reenergized only after reverse operation has been stopped and the PTO switch has been moved to the off position.

Abstract: An overheat protection circuit includes a resistor having a first lead connected to the engine temperature switch and the power take off (PTO) relay coil circuit. The second lead of the resistor is connected to the output of an interlock circuit to provide an energizing voltage signal to the PTO relay for operation of the PTO driven attachment when preselected operating conditions are present on the vehicle. If for any reason the engine temperature rises above a preselected maximum operating temperature, the engine temperature switch will close and cause the voltage at the second lead to drop below the minimum operating voltage of the PTO relay. The PTO relay deenergizes to remove drive from the attachment. The PTO cannot be reengaged until the engine operating temperature drops below the maximum operating temperature. The resistor preferably is a positive temperature coefficient thermistor to reduce power dissipation through the circuit while the temperature switch is closed and the PTO relay is deenergized.

Abstract: An interlock circuit includes key and PTO switches, at least one operator presence switch, and relays connected to a transmission switch to prevent engine starting and running unless the PTO is off, the transmission is in neutral and the key is on. Operator presence switch activation is unnecessary to start the engine but is required before PTO or transmission condition is changed to begin a vehicle operation such as cutting grass. Required start and run features of the interlock circuitry are met using simple circuits with readily available components and without modules. The circuitry can be used with pull start and electric start vehicles and is particularly useful with vehicles that have transmission clutches that lock engaged when the operator releases a bail.