Need a specific wiring diagram? Search for "Cat C4.4 Electrical Schematic (SENR9970)" for your serial number prefix (e.g., C4Z, T40, JLB).
On Common Rail engines, turn the key to the "ON" position (do not crank). You should hear an electric lift pump (located on the fuel filter base) run for 2-5 seconds. cat c4 4 troubleshooting manual
If you have the older MUI engine:
A lack of power (derating) is often linked to the turbocharger. Need a specific wiring diagram