ELECTRICAL AR 1607092 - Caterpillar

Engine Overspeed (OS)
When engine speed increases above the overspeed setting (118% of rated engine speed) of the electronic speed switch (ESS), the overspeed switch ESS(OS) will close across terminals ESS-8 and ESS-7 (line 29). This completes the circuit from the battery through crank terminate ESS(CT) switch across terminals ESS-11 and ESS-10 (line 13), through ESS(OS) switch to both slave relays [through diode (D2) at line 31 to SR2 (line 33) and SR1 (line 36)].Both SR1 and SR2 are now energized at the same time. SR2 will close across contacts SR2-1 and SR2-3 (line 47) to connect the magneto (MAG) to ground and stop current flow to the spark plugs. At the same time, SR1 will open across contacts SR1-1 and SR1-2 (line 45) and close across contacts SR1-1 and SR1-3 (line 43). The gas shutoff valve (GSOV) at line 42 is now energized (ETS) or de-energized (ETR), and will now shut the fuel off to the engine.
Unburned gas left in the manifold can ignite when the engine is restarted.
Before restarting any gas engine which was stopped by grounding the magneto, crank the engine with the gas valve turned off, and the magneto grounded, for 10 to 15 seconds. This will clear the unburned gas from the exhaust system.
To avoid engine damage, repair or correct the problem that caused engine shutdown before restarting.
A reset button on the ESS must be pushed to open the overspeed switch ESS(OS) before the engine can be restarted.Coolant Overheating
The current flow for the circuit discussed here is for an engine that is running at any speed with coolant temperature hot enough to close water temperature contactor switch (WTS). When WTS (line 18) closes, the circuit is completed across terminals TS-2 and TS-7 (line 18), through diode (D3) at line 19, through jumper between TS-9 and TS-10 (line 21), through time delay contacts TD-6 and TD-7 (line 36) to slave relay (SR1) at line 36 and (SR2) at line 33.When SR1 is energized, the switch will open across contacts SR1-1 and SR1-2 (line 45) and will close across contacts SR1-1 and SR1-3 (line 43). The gas shutoff valve (GSOV) at line 42 is energized (ETS) or de-energized (ETR) to shut the fuel off to the engine. The starter motor circuit can now be engaged, but engine cannot be restarted (no fuel available) until coolant temperature drops below WTS switch rating, when the switch can open again.Relay SR2 is also energized and closes its normally open contact (line 47) to connect the magneto (MAG) to ground and stop current flow to the spark plugs.2301 Electric Governor Control System
When the 2301 Electric Governor Control (EGC) is used, all components of the protection system are activated in the same way as discussed with the nonelectric governors.With this circuit, current normally flows from TS-28 and TS-31 (lines 43 and 44) through preregulator (PR) at line 48 or fuse (F4) into the EGC. When the engine flywheel is in rotation, current also flows through electric governor actuator (EGA) at line