On a 1999 Ford E-150 with a V8 engine (the most common configuration), cylinder 6 is located on the
passenger side (right side) of the engine, towards the rear. Think of it as being towards the back and slightly to the right of the center of the engine block when viewing the engine from the front of the vehicle.
It's important to note that this is a *general* location. A specific diagram of your engine would give the most precise location. You can often find these diagrams in a repair manual specific to your vehicle's engine (e.g., a 4.6L, 5.4L, etc.).
