DIAGNOSIS The switch light coming on tells you power is reaching the switch, but the signal isn't getting to the blade relay or the PTO clutch itself. A blown fuse is the first place to look.
FIX You need to check the PTO fuse. 1) Turn the key off and remove it. 2) Open the main battery compartment behind the seat. 3) Look at the fuse block—it's a small black box with a clear lid. 4) Find the fuse labeled for the PTO (it's often a 20-amp or 30-amp). 5) Pull it out and check if the little wire inside is broken or melted. Swap it with an identical spare fuse from the kit that came with the mower. 6) Try engaging the blades again.
IF THAT DIDN'T WORK The next thing to check is the PTO clutch air gap. Over time, the gap between the clutch electromagnet and the armature can get too wide. This requires a feeler gauge and adjusting the mounting bolts, which is a bit more involved but a common fix.
HEADS UP Always make sure you're fully seated when testing the blade engagement. The system is designed to prevent the blades from starting if you're not in the seat, which could mimic this problem.