Left-hand and right-hand are referenced from the point of view of the tractor operator.
The flat backside of the belt rides on flat idlers; the inside vee rides in v-idlers and pulleys.
Bring the belt forward over the frame cross member and steering sector gear on the lefthand-side of the steering shaft. Snake it around the belt guides and onto the top engine pulley (#1).
Loop the back end of the belt around the transmission pulley (#2).
Set the parking brake to provide slack in the belt and route the belt around the three idler pulleys and inside the belt guides (#3, blue).
The front of the idler tensioning spring hooks into a hole on the idler arm (#4, green). The back end of the spring hooks onto the frame (#4, blue).
Husqvarna LTH1538 deck belt. Be sure the belt is within the belt guides (#5, blue).