Traced the wires between the Audio panel and SL40 and confirmed wires had continuity. Found that one of the pins on the Audio panel was in the wrong D-Sub pin slot and removed and reinstalled in the proper pin slot. Tested and all works.
Also downloaded the GTN650 installation manual to find out which High density Sub-D connector I need to remove to add an additional RS232 GPS-out for the Transponder 2020 mandate.
