Here are three obscure Plane-Maker/X-Plane features that can save you time if you developer complex aircraft.
Plane-Maker Will Copy Your Instruments
You may know that in Plane-Maker, you make your own copies of X-Plane's PNG files to customize the look of the instruments. But did you know that Plane-Maker will copy the images for you?
Select an instrument and type Control-P (which is the default for the command binding "pln/panel/copy_instrument_png"). Plane-Maker will copy all PNGs for that instrument into your aircraft's cockpit or cockpit_3d folder. This can save you the time spent wading through X-Plane's cockpit folder to find the right PNG files.
X-Plane Can Make a Panel Image for UV-Mapping
When you are making a 3-d cockpit, you use the 3-d panel as a texture. But how do you know how to UV-map this texture in your cockpit? Often the panel background (panel.png) is blank.
X-Plane can make a snapshot of your panel for you, in the exact size you need to UV map. Use Control-Alt-Shift-Space (Command-Option-Shift-Space for Mac nerds) to run the "sim/operation/make_panel_previews" command in X-Plane. It will make a PNG file in your aircraft called Panel_preview.png - it's just like Panel.png but with the instruments drawn in - perfect for UV mapping.
Plane-Maker Will Tell You What's Wrong
That sad face icon in top bar of the Plane-Maker panel editor enables "warning" mode. In warning mode, every instrument that has a potential problem gets a red outline. Select one instrument with a red outline and in the upper left corner of the panel you'll see a description of what's wrong.
This picture on the left is from Plane-Maker editing a 3-d panel. (That's why it is just a "packed" set of instruments with no background; this panel is used as a texture for a 3-d cockpit - each instrument is UV-mapped into the right location.)
The air-speed indicator has been flagged as having a problem, and the text shows it. In this case, the lit texture has an alpha channel, which causes the lit texture to draw incorrectly. Fix the texture and the warning will go away.
I strongly recommend checking all Plane-Maker "red boxes" on your plane - most of the warnings will tell you about problems that would otherwise be very hard to detect.