We have a 3512b running one of our emergency generators offshore and have got problems with the unit not shutting down. When you press stop on the gen control panel the engine goes from 1800 to 900rpm for a 60 sec cool down but will never shut down. Hooked cat et up to it and the 60 sec timer never counts down when it does go to cool down only way to stop it is to turn the engine control panel switch to off. All we are sending it from the gen control panel is a pulse signal to a relay which is getting it checked with fluke all signals look good to the engine. Any advice?