Make sure your gps connection cable is only using pins 2,3 and 5. If you use a null-modem cable with all wires connected you could be grounding out the system. Ag Leader chose to also put power to that connection and if you have the wrong hookup it will cause problems. It has been too many years ago to remember all the specifics but I remember using an ordinary null-modem cable from the gps to the PF3000 with all 9 wires connected and it cuased the monitor to blank out.

John