Make sure that you have the RIGHT cable! I used my ez 500 w/ my Agleader monitor this spring, when I hooked up the Null modem cable I kept blowing fuses, come to find out that the Ag Leader is connector is pinned a certain way so I was getting feedback from the ez guide. Once I had the right cable evewrthing worked great, took about 20 fuses to figure this out.
Good Luck