wiring problem John Deere L120?

I'm having a problem with my John Deere L120 lawn tractor. It began with a blown fuse which melted the electrical box to engage the blades and shorted the mower out so it wouldn't even run. I have since replaced both the fuse and the switch/electrical box for the blades and the tractor itself runs fine. However, every time I try to engage the blades it causes the tractor to die (like it's shorted out). Any suggestions or advice would be appreciated.

Thanks