Gear Warning Horn Wiring Inop

[MarkM20C]

   Hello, I have what should be a pretty easy to figure out problem, but could use help from Mooney Space. My gear down warning horn has always been a little sporadic, but now has quit altogether. I can hear the switch on the throttle cable clicking when throttle is pulled towards idle, and get 12v at that switch when gear isn't locked down. What seems strange to me is that the switch on the throttle cable closes when throttle is advanced, so I get 12v from throttle cable switch when throttle is advanced, not when throttle pulled towards idle. In looking at the wiring diagram, seems to me that throttle cable switch should close when throttle is pulled to idle (or approx. 12mp), not when throttle is advanced. Seems like my throttle switch is working backwards, but either way the horn doesn't work and used to (mostly) and nobody has messed with the wiring.  Any ideas?

Thank You, Mark

[PT20J]

I'm not looking at your schematic, but assuming that the gear warning is a sonalert, if 12v were connected to the sonalert and the other side ends up grounded by the throttle switch then the switch would have 12V on it when open and 0V when closed as you describe. I would suspect the sonalert is bad since you say it has been flakey. 

Skip

[carusoam]

Nothing like getting the voltmeter out to chase the wires from one end to the next…

Could be a dirty connection easy to access… or one in the ceiling, harder to access…

Being ready to replace the sonalert and fix things at the same time while the sealing is out may be helpful in the long run… air vent control and drain usually need some help around year 35 to 50… 

Starting near the throttle switch and gear position switch is pretty easy…. 
 

PP thoughts only, not a mechanic…

Best regards,

-a-

[MarkM20C]

Thank you, I'll look at it that way. According to the Maintenance Manual, the throttle cable switch supplies power to the gear horn and the horn has a ground. But seeing how its 56 years old, who knows what has been changed! When trying to figure out why my tail light didn't work, found wiring not even connected! I guess previous owner never flew at night?

Mark

[MarkM20C]

I'm looking at the ceiling thinking I really don't want to take that apart. Plane is sold, so I want to fix for new owner. I'm an A&P so don't worry, repairs will be legal. I don't work as an A&P, but I am licensed. I don't think I could afford to own an aircraft if I wasn't!

Mark