I have a D120 installed in a RV7-A. The aircraft has not flown although the engine has been run 4 times. Initially the CHT readings appeared to be accurate. I now have a -9 reading on CHT #1. This reading is the same whether the engine is running or not. I have checked the wiring to #1 CHT and have good continuity to the D120. I also swapped the sensor with #3 CHT and the #1 sensor gave a good reading when connected to the #3 Wiring. The #3 sensor connected to the #1 wiring then registered -9. Seems to me the D120 is at fault, can you give me a suggestion to resolving this problem?
Did you check to see if any of the wires are 'retracted' at the Dynon connector end ?
Although they may appear to be ok refitting the connector can cause issues especially IF you bend the harness in any way while doing so - hold the connector in one hand and wriggle the harness with the other, you'll see what I mean.
FWIW I've never had cause to ship a unit back to Dynon due the symptoms you have but I did some head scratching until I worked it out.
From my experience (have done many installs of dynon equipment) the issue is due to the inherent stiffness of the thermocouple wires and how the backshell is fitted. the wires at the outermost ends of the connector are usually at fault but some of the others can come into play as well.
What seems to happen is the wires are 'pinched' together when the assembly is done causing a lot of strain on the pin sockets in the connector sometimes resulting in damage. Moving the harnes as mentioned will demonstrate what I mean, the pins will move in/out like pistons.
There is a fix for this situation, which is better done before installing the harness. What I do is remove the backshell & heatshrink, carefully bend the outermost wires towards the centre of connector & reassemble - problem goes away
HTH
Jake J