When my 4250 started doing that several years ago, the service manager at the local Deere dealer told me that the later model 50 series didn't have the temp warning sensor anymore.  He told me to unhook it and forget about it.  I don't remember if I had to jump the wire to shut off the light or not.  It's been a few years ago.  The oil wasn't getting hot and it hasn't been a problem since.