B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 232
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Maintenance Action
Procedure
During my preflight flow I discovered that neither stall warning system would test. We check all appropriate circuit breakers and they were all in; so we called Maintenance and relayed our situation to Dispatch. Maintenance tried everything they could think of; including completely powering down the aircraft; but neither system would test; which we all thought was highly irregular.I let Dispatch know; and as they were in the process of determining how to proceed with our flight; the Technicians summoned us to the cockpit and seemed to be very surprised. They had discovered that the cannon plugs had been DISCONNECTED from the underside of BOTH STICK SHAKERS. This condition was very hard to detect from the seated position in either seat. And why would either the First Officer or I even look to see if that had happened? I have to say that we were all shocked; to say the least; and had serious questions as to how this occurred.The plugs were reconnected and both systems tested normally. The logbook was signed off; and we departed after being delayed for over an hour. The FO and I discussed what had happened and ended up having more questions than answers as to how such a SERIOUS condition could have resulted. The COMPLETE DISABLING of an aircraft WARNING SYSTEM is something that I've never encountered in my career.
[Report narrative contained no additional information.]
B737 flight crew reported that inoperative stall warning systems noted during preflight were due to disconnected stick shaker cannon plugs.