Do you have an F18 (two-wheel drive) or F18D (four-wheel drive)? F18D has a very obvious, short lever on the left side of the transmission hump, near where your left heel rests when not pressing the clutch. Just press your clutch down, slide the lever to 4WD and away you go... Just be sure to put it back into 2WD whenever you're on hard-pack, pavement, etc...