New to us 1900 air cart and 1820 hoe drill.  Works well most of the time, but sporadically loses communication with air cart.  Have to shut tractor off and then reboot.  Tractor is using the armrest display (no 2600/30). Cart uses brown box display in the armrest controller.  Voltages out from the tractor test okay.  (13.5-12.5 running vs off).  I replaced the harness from the tractor to the box on the front of the cart, and it helped some.  It now seems to boot up all the time, as before you might have to restart the tractor four or five times.  So, do I have a software issue, or do I need to order the harness and actually install a separate brown box display in the tractor? Thanks for your insight.