GAUGE AND SYSTEM AIRCRAFT
The GaugeAndSystemsAircraft aircraft is a preset of the WASMAircraft modular aircraft, which shows how to create a WASM systems module for a plane in Microsoft Flight Simulator 2024. Once the WASM Aircraft package has been built, this module will be available for flying from the aircraft selection screen:

The WasmModule.sln file will allow you to compile the code with Microsoft Visual Studio (2019 or 2022) in order to create the GaugeAndSystemsModule.wasm WebAssembly module which will then be loaded by the game. Once compiled, the module will automatically be copied into the following folder
..\PackageSources\SimObjects\Airplanes\MyCompany_Wasm_Aircraft\presets\mycompany\GaugeAndSystemsAircraft\wasm
In order for the aircraft to use the systems module, it has to have been registered in the systems.cfg file found in the Config folder, using the [WASM_SYSTEM.N] section of the file:
[WASM_SYSTEM.0]
ModulePath=SimObjects\Airplanes\MyCompany_Wasm_Aircraft\presets\mycompany\GaugeAndSystemsAircraft\wasm\GaugeAndSystemsModule.wasm
SystemName=Sensor
As can be seen above, the system module is referenced using a URI relative to the PackageSources folder location.
Note that if you make changes to the C++ code and recompile the WebAssembly module, you will have to build the modular aircraft package again. This can be done while the plane is used within the simulation.
Testing
Once you have built the aircraft and selected it, you can go into a Free Flight and you will see three panels in the cockpit:

The third panel is the same as that in the VarsAndEventsAircraft, and the first two panels look identical to the panels shown in the GaugeAircraft, but have been setup differently. In the Gauge Aircraft these panels have code to do calculations included in the gauge modules, whereas here we have the system module doing all the calculations and then sending values (pitch, bank, and heading) to the gauges. The gauges themselves are simply drawing to the panels and nothing else.