Back story: Plane finished in 2014, flew great for 2-3 years. I'm pretty sure I did a software update on the dynon transponder and the next day when I went to fly, prior to take off I noticed it said there was no GPS position. I changed the transponders position input to the GPS250 and have been flying it that way since. When it first occurred I researched and called dynon and they said the wire is broken. I didn't believe that since it worked fine the day before but I checked and couldn't find a loose or broken wire anywhere. End result I gave up working on it. Today I dug the wire out from the GTN connector to the dynon connector and even cut open my heat shrink and replaced the resistor. The wire wasn't broken but I was hoping it was fixed. NOPE, same sad story. I called dynon and they suggested maybe a firmware update or possibly the transponder has an issue. I tried the GTN on both of its ADSB-B+ formats which is only selectable under the one serial pin I used. I know the wire is good so its getting to the transponder or at least I think it is. However, if I select it as the source under the transponder setup it still tells me GPS offline. Tomorrow I'm going to try a spare transponder I have to see if that is it but is there anything I'm missing here...Its only the one wire between the two. The GTN and transponder work flawlessly otherwise and it worked fine for the first two or three years. Any help or ideas would be greatly appreciated. Thanks