What is this, and is it important?

[Peter B-SKO]

Just brought home my bus. 1998 thomas with a cat 3116. Poking around the engine compartment I found this big black box and have no clue what it is. Any help would be appreciated.

 

[aaronsb]

That's the controls for starting the engine from the engine bay. Not sure what other magic is in that box though.