I have a 1946 chev. fire truck pumper that I am restoring. The tach is for the operator who stood either along side the truck to operate a front mount or side mount pump. The button was for the siren.
The front mount pump would have been mounted off the front of the truck & ran off the front of the engin connected by a PTO from the lower front crank shaft pully. The mid ship pump would have been run the transmision. You could check and see if there is a side plate where the PTO box ran off the transmission.
