Dometic 5 Button Thermostat Lost One Zone

Hi Doug, First thanks for the info. My RV is a 5th wheel Montana 3615 RE I checked the phone cable. The rear air conditioner has 2 cables and the front has one. The way it started was last week my wife came to me and was worried that the digital display didn't show zone 1. I turned off thermostat and turned on and there it was. You couldn't set temp just showed fan auto and cool and temp. I did the reset this week by holding mode and zone till ff showed then released now the thermostat only shows zone 2 rear. I used your idea and checked zone 2 and sure enough there was 2 phone type cables plugged in. I removed and reinserted several times. They didn't look corroded. I then went to zone 1 and did the same thing to the one cable there. Did not help. Reset thermostat but still does not show zone 1. If it means anything besides a 10 cent cup of coffee but I worked for 35 years in electronic/mechanical repair. Some on e said there was a problem with cold solder joints on this thermostat but could be anything. Any ideas you have would be greatly appreciated. Don't know if they are penquins