Debugging wiring

Most wiring mistakes fail quietly. Check in this order.

Issues panel. It flags outputs aimed at a targetname no entity has, and inputs the target's class does not have. A typo in a targetname is the most common reason a door stays shut.
Logic panel. It fires an output on paper and shows the whole chain, see Placing and wiring.
F3 in game. Add a GodotTrenchDebugOverlay node to your scene, or as an autoload. F3 lists outputs as they fire and draws every Area3D volume with its targetname, which tells you whether a trigger never fired or fired at a target that does not exist. Volumes are collected when the overlay turns on, so toggle it again after spawning triggers.
Code. GodotTrenchIO.events() emits fired for every output, including ones whose target resolved to nothing. A logic_debug entity with trace_all set to 1 logs the same without code.

GodotTrenchIO.events().fired.connect(func(source, output, target, input, parameter):
    print(source.name, ".", output, " -> ", target, ".", input))

What each mistake looks like

Mistake	Symptom
Target resolves to nothing	Nothing at all, no warning
Target has no such input	`[GT I/O] <node> has no input '<name>'` in the Godot output
Output the entity never emits	`[GT I/O] <node> has no signal '<output>'` once, when the map is built
Entity spawned or renamed at runtime	Not found by its targetname, see Targets