HVAC control module pin out needed?

Very doubtful of you finding any board level schematics, those are only shared with the folks who make the boards and a very few authorized repair companies. However, the wiring pinouts are attached. First is the automatic system, second is manual control. What is the issue you have? GM systems are generally known for failing aspirators and actuators, with the occasional control head failure. The connector images fit both but with some missing on the manual control.

Usually, a resistor failing is from a motor pulling extra current. GM (and others) have always had issues with the blower grounds. I would like to add a second one, when possible, simply because of that. Light wise it depends, the older modules are picky about the current load from lighting, the traces tend to heat and curl. The newer ones with LED just have the voltage regulator fail because the no lead solder cracks and you get strange results depending on which one is cracked.

Usually, a second ground for the blower motor as short as possible. Then I like to make sure the body to engine and body to chassis grounds are still good. GM used ground straps that rot off for those.