Dang. Lost my last post
I believe models up to 74 have a dual stall/gear warning system. It looks like the box has two speakers out of it. Found it yesterday. Just under the pilots right knee in the center console will get you access to the back side of the box. Speakers face copilots side. If both speakers fading, might be a grounding issue. I believe its the brown wire coming out of the box. Follow that and clean up the ground point.
I think newer models moved the dual warning box (not sure where) and ran the audible through the overhead speaker. Might be worth checking the ground, speaker condition there too. Cardboard cones don't last.
Not to steal this thread but we've been chasing a somewhat similar issue. Service manual says the green gear indicator light you can push 'midway' with throttles at idle and do a audible warning test of the gear warning system. So far no success on getting that to happen. The button/green push to test works fine but it doesn't feel like it has a midway point. Didn't get time to really dig into the troubleshoot. Going to check throttle body microswitches today...