I have a New Holland Boomer 47 tractor. The tractor was parked in the barn, we use it daily. I went to start it, the tractor clicked then no power at all to the dash and other functions. I checked the battery terminals and cleaned them. The battery has a full charge, changed the ignition switch because the start function stopped working a while ago, used an intermittent switch. I thought the ignition switch had just gone the rest of the way. I am getting 5 volts to the switch but when I turn the key on nothing happens. I messed around with the parking brake, seat safety switch, to no avail. i checked all the fuses I could find and none were bad. I had a glimmer of hope when I shifted from 2-wheel drive to 4-wheel drive, everything lit up on the dash and the glow plugs turned on. When I turned the key to start everything went dead again, I haven't been able to recreate it since. Any help would greatly be appreciated. I feel like I am missing something simple.