installing the G1000 MFD replacement mods.

[adminOwner2]

After MSFS loads in flight, it takes about 2-3 minutes for the WASM gauge to compile. After that the screen should light up.
But in your case, since the PFD is missing, most likely the mod or another component are not installed properly.

Do you get any error messages pertaining to the TDS GTNXi or the C172 in the Console of MSFS which can be accessed from Developer Mode?