If Gillig it is EPM
The Gillig chassis if with CAT engine for sure, not sure on the others, will have an engine protection module that will sound an alarm if high temp, low water or maybe some other issues, you have about 15 to 30 seconds before the fule is shut off.
The foot switch stops the delay timer.
More data can be received from Gillig, they can provide prints and manuals after you give them your VIN.
The module may be under the dash, if you unplug it the engine will not start, wil crank but not fire...do not ask how I know this...