Deere 4100 blows starter/glow plug fuse when pulling pto switch

[coloradotrout]

I had been mowing for an hour when it suddenly died. No dash lights, nothing. I found that the 10A fuse was blown. I replaced it, started right up, but when I engaged the PTO switch, the fuse blew again. Later I installed a 7.5A fuse and mowed for about 30m before the fuse blew. Hydraulic fluid is at minimum on the dipstick. I do have a leak at the fitting attached to the pump. The finish mower was working hard but not stalling.

What can I check?