Because of the variations, the best way to find it is to:
1. Consult your owner's manual: This is the most reliable source. It should show a diagram or describe the location.
2. Look carefully around the bottom of the engine block on the driver's side: Start by looking near potential drain plugs or similar fittings.
3. Trace the cord if you find a connection: If you spot a heavy-duty cord attached to the engine block, follow it to find the plug.
If you can't find it after a thorough search, it's possible the truck might not be equipped with a block heater, especially if it wasn't purchased or used in a particularly cold climate.