Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Deere safety switches are the seat, and brake and pto switch. They make up the run circuit. Check the seat switch and harness, and the continuity between the other safety switches. Your run circuit is not complete, so engine is killed when you engage the blades. The mower thinks that there is no one in the seat. (safety circuit)
This is wiring for the old 180, same as 170 and others.