I have a Narco AT 150 transponder and a King KN 64 DME, which often reply to each other's signals.  A suppression wire was installed between the two radios to eliminate this problem.  The problem that I have is that although the units no longer reply to each other's signals, my Mode C cuts out, according to Air Traffic Control.  Is this a King issue, Narco issue, or is it an encoder issue.  I know that the Narco transponder has a positive suppression pinout and a negative suppression pinout but I'm not sure how this affects suppression. Any ideas?