Will this Battery kill switch work on a semi truck?

Same. Grote has one too but I’m not sure if sell grote in the USA. I always put mine on the ground side.

 

Yes. Grote is big in U.S. they been an oe supplier since the beginning.
Grote makes a lot of private label stuff for Fleet Pride in the states.

 

Here is a short video of how to test your diode pack in the alternator. The meter he used, is the simple, and cheap Harbor Freight multimeter. Anytime you see the icon that he set it on to test the diode, that meter will work. A diode is a one way power gate. It is designed to allow power to get out of your alternator to the batteries, but not return to the alternator. If the diode or diode set/pack etc., is bad, then when the key is off and the engine is stopped, the alternator field is still being energized which, the larger the alternator, the larger the draw will be. Usually much more than "parasitic".

You can use that same meter to find any other power draws as well. Here's another youtube video explaining this.

 

Quick and dirty check. After the truck has been sitting for several hours and everything is cold, check if the alternator is warm. If it is and everything around it is cold, very high possibility a diode is shorted and allowing current flow in reverse-bias.