The Homestretch!

More wiring and then an issue. After I had wired up a number of engine probes, as in picture one, I wanted to see the results on the avionics. Mostly it would show zeros for pressure instruments but temperature instruments should show the room temperature.

I turned on the avionics and a number of things worked as expected but only one of my CHT probes seemed to work. I then temporarily hooked up the EGT probes and two of those worked ok. Since some where working I thought I might have damaged some wires or the box they connect to but I wasn’t sure how. It was also possible that the box was malfunctioning which would then need to be replaced.

After trouble shooting with a temperature bath to get them all to the same temp and double checking that there was no calibration step needed, I called Stein, my avionics and wiring supplier. These wires are in a bundle that Stein had wired up. After talking with them they suggested that I check for an off by one error in the cable pins.  As soon as he said it I was sure that was the problem and I looked up the schematic and realized that I could predict which pins would be in the wrong place. There was two possibilities that would explain the symptoms.

The problem then was that I never expected to have to regularly remove this connector and it was tightly secured in the wire bundles. With some careful unbundling I was able to get at the connector and could see a missing pin at one of the predicted locations with the five adjacent pins all offset by one position. All I had to do was move those five pins one by one. Picture two shows the missed hole.

If the connector was out of the airplane on a bench it would be a job of a minute or two. In place in the aircraft, it took almost a half an hour of struggle and a little more to get it back and installed.  Picture three shows the back of the connector after one pin has been moved. When I got it done, I was greeted with the screen shot in the last picture. All the temperatures within acceptable tolerances.  The top numbers in the yellow field will average around 300 to 400 degrees while the bottom numbers could be as high as 1600 degrees.