Well, it's a shut-off valve, either for the fuel or for the gas (they're basically identical valves). Based on the location, I'd guess it's the fuel valve.
Easy to establish if it is fuel (Diesel) or gas... turn it off and see if it takes longer to boil the kettle! Seriously from the location it looks more like the fuel isolation valve. Nice placement really, need to squeeze past a burning engine to isolate the fuel supply!
Looks like the fuel shut off valve, But what is the wire bonded to? The bracket is insulated with rubber...