WHAT PULLEY DO I loosen to get single drive belt on?

If you are referring to the Serpentine belt, you loosen no pulley. You simply remove tension from the belt. The tension is applied by the Idler Pulley. Pry the idler back and remove the belt.

If you are referring to the Serpentine belt, you loosen no pulley. You simply remove tension from the belt. The tension is applied by the Idler Pulley. Pry the idler back and remove the belt.