Mark

I'm still trying to get the flow of this.

Is Nav Tuning from the Garmins or is there separate Nav Control Units?

If the Garmins are tuning, it looks like those tuning requests go to the DME Master Indicator (KDI-574) on pins 11, 12 and the J-Box on 70, 51. from there the J-Box feeds the request to the DME (KN-63)  on pins F, 6. The DME output goes back to the J-Box which feeds the Arinc Adapter (KDA-689) which outputs 429 data back to the GNS (I only see an output to the left unit).

If I'm correct, this still leads back to a tuning issue from the #2 (or right) GNS. I circled some wires to check on a previous post. The "RNAV REQUEST" signal from each Garmin looks to be the signal which tells the Master Indicator which side (GNS request)  to forward to the DME.

If those four wires (18, 19, 20, 22) check good from the #2 GNS..... the Master Indicator would be the most suspect unit.

Also, three of those wires are connected to each other via splices. To make sure one Garmin isn't loading them down, try each alone with the other GNS not in the system. In your case.... disconnect the #1 GNS to see if the #2 tunes and displays properly.