stall warning horn

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    This is probably a can of worms I am opening, but, I have to cast a line out there to see if anyone has experienced this ‘magic’ before. We recently acquired our 310C model (PS – love it) and unbeknownst to us the plane has sailed through the last few annuals with a squawk that I cannot believe wasn’t caught – the stall warning horn is INOP. As a matter of fact, I cannot seem to locate same. In the manual it says that a light and horn combination reside in the dash. The spot where it should reside contains an AUX fuel gauge for aux tanks installed when the underwing exhuasts were installed by STC. I have carefully inspected the wiring at the switch and there are only two wires going there. The switch operates nominally (when it rises, it closes the contact e.g. completing a circuit to a warning horn, should I be able to locate one.) One wire *should* be carrying positive voltage. It appears to come into a small ‘cylinder’ attached to the switch itself (perhaps a heating element?) and then looped to a ground lug on the switch itself. The other side of the switch has a wire that comes all the way inside to a bus bar by the pilot’s leg (top row, sixth from the right IIRC) where another wire leads to who knows where. Now, it didn’t seem that there was any voltage AT THE SWITCH when I powered on the master. I think there should be power there, and the closing of the switch completes a circuit to a horn (if there is one!)

    Any opinions? Should there be power at the switch in the wing? I cannot imagine a scenario where this would be a resistive type setup, although I am willing to concede that *could* be the manner in which it is operated. However, that would leave me to believe that the horn woudl be connected to something else to provide power.

    HELP! Incidentally, the service manual and parts catalog are not much help.


    It is not resistive. It is powered. My mistake was assuming that power was coming from the switch. Turns out, both lines to the stall warning switch are powered. The switch itself, when being actuated, is slowing bringing a ground into the circuit.


      I don’t know specifically about the 310s, but all the 340, 414s, and 421 that have a normal stall warning and not an AOA are wired the same. The 28 volts goes from the CB to the transducer in the leading edge. The other side of the transducer is run to the horn. The other side of the horn is grounded locally. Very simple setup. Problems occur in the old horns not working correctly or the transducer is not making contact or some bad wiring. The small cylinder attached to teh transducer is indeed a heating unit which is powered through some switch makred stall warning heater or some such name.

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