Purchased and installed a Dynon 261 transponder. I bought the version without the wire harness. It did come with a D-sub connector, pins and a black plastic hood that I was not familare with. When I wired and installed the transponder, I got a transponder fail mesage on power-up. after spending the day chasing wire routing and software set-up, It turns out that its possible to assemble the D-sub hood wrong. The hold down screws need to be in the chanel aft of the gap behind the connector. Else the screws stick out too far and bottom in the transponder receptical befor the pins are seated. I'm glad I finilaly got that figured out.