I have the same harbor freight meter as a part of my survival tool kit. Mine reads close to a commercial Fluke meter. I got lucky.
The Pantera amp meter is known to bounce around alot. That is also covered in the threads of the forum.
I changed gauges to Auto Meter and the amp meter is now a expanded scale volt meter. I feel the information is more relavant.
Still would not hurt to make sure connections are clean and secure.
The front compartment has a stud welded to the chassis for a ground connection. The engine has a ground strap at the rear of the transaxle. The voltage regulator (stock one) is in the right rear wheel well , could get wet and corroded connections. There is also a common ground stud under the dash that can be problematic. I would think the under the dash ground would affect things in the cabin and dash mostly.
Panteras are known to have electrical problems. This forum is a wealth of great information.
Without starting the engine and no load I would expect more like 11.5 to 12 volt with a well charged battery. Starting the engine at curb idle the voltage should climb to 13.5 to 14.7 volt.
Harbor Freight also has a automotive test device that has a series of leds that show approx. voltage. A whole $4.49.