There is some kind of electric device attached to the front of my Cat 3208 out of my 77' C8000 where the tach cable attaches. What is this electrical thing? What does it hook to? And is it critical for anything? Mine has a split in the case and the wires were cut when I bought the truck. I attached pictures to show what I'm talking about. Thank you in advance for your help.
Fire truck have two tachs, one in the cab (factory) and one on the pump panel for the engineer to monitor engine speed while pumping water. The adapter you have most likely sent a signal to a electric tach on the pump panel. This adapter would be an aftermarket add on by the company that built and installed the pumper body.
Fire trucks also had oil pressure and water temp gauges on the pump panel so you should have extra sending units on the engine for those unless someone has removed them.