I believe I may have identified the problem.
I had noticed earlier that both the positive and negative power supply wires felt really hot - more than they would be from the hot running compressor. Looking closer at the male/female connection (hate those spade connectors!) at the compressor I was real suspicious of what appeared to be overheating
at one end. This was a 10g. wire that I had run about 24" from a terminal strip that serves the refrig. Measured voltage at the terminal strip was 12.9V. Couldn't safely get my probes into position to measure voltage directly at the compressor.
I also got my first red fault indicators this morning. Once for a failure of compressor to start, and later for low voltage
The underside of the connector appeared a bit darker than the part that was easily visible. Measured resistance was about 1.9 ohms of this wire portion. Replaced the wire with a new connection using 12g. (since that was readily available without searching throughout the boats lockers).
The result appears to be that the system is working properly. Wires are normal temperature, no fault signals, and running in auto mode without any issues.
This raises another issue and that is push-on spade terminals. I don't think that they are safe. Seven or eight years ago I had a push-on terminal overheat and catch fire (Wow did that catch my attention!!) on the small heat pump HVAC
system we have. I have never had standard ring terminals fail unless they were immersed in water.
My thoughts are that many of these systems are intended for dual use in the RV world and corrosion
due to salt
air is not given the necessary attention by manufacturers. Push-on connectors are inexpensive for the manufacturers and take up little room. They also make it difficult to get probes safely in for diagnostics.
The take away from this? Check all push-on terminals.