JD 4310 electrical problem?

[Gator41]

Hey guys, new guy here with a strange problem. Ive got a JD 4310 ePowerReverser tractor, about 430 hours, has always ran great. The other day, it quit while mowing, blew the F5 fuse. I ran the wiring harness, cant find an open, but discovered (by chance) that if the MFWD switch is off, and you turn the key, the F5 (20A) fuse blows. If the MFWD is ON, the tractor starts and runs fine, but if you turn off the MFWD switch, the F5 blows and tractor dies. ??? This has never happend before, Ive used MFWD with no problems in the past, and no other fuses are blowing. One of the K relays bad, switch bad? I was going to d/c the starter to see if the fuse blew, but then I found it starting with the switch on, so it cant be the starter, right? Is this a transmission problem? Im running out of ideas. My local JD place had no idea on the phone, and I cant send it to the shop right now. Any ideas, gurus? Thanks in advance.

 

[beenthere]

Put a 12v light bulb in the fuse spot (I solder a couple leads to a bulb and to a blown fuse).

When there is a short, the light will be bright, and dim when no short.

This has worked well for me tracing out a short (which you must have) in a circuit. It saves on fuses and frustration.