Strange readings on EGT 1 and 2

Have a 915iS in a Sling.  Had a sudden rough running engine issue about 1 hour into a cross country flight, Lane A solid light.  Landed, checked a bunch of things, no smoking gun, problem didn't re-appear on restart or anytime afterwards, so I'm chasing an electrical gremlin.

Download of BUDS data revealed very strange values for both EGT1 and EGT2 - sometimes flatline, sometimes bouncing around.  EGT 3&4 looked normal, and EGT 2 worse than EGT 1 until they both became noise.  Given the probes for EGT 1 and EGT 2 are on separate sides of the engine and go into separate dual input "packs", I'm thinking it's possibly somewhere upstream in the wiring where they might converge.  I can't locate a wiring diagram for the 915is that is detailed enough to show things like what pins on what connectors these would be on the fusebox and ECU.

I can upload BUDS data if needed.

Anyone point me to a diagram, or have some input on things to check?