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Whose thermostat are you using? Not familiar with a "6400" as such by that number.
I am not familiar with that for RV use, so I will opt out of this question and let another tech offer something. I like to stick with the brand of the A/C so I know it will work without modifications.
I see nobody responded here. See the attached link and tell me if this is what you are trying to hook up here? https://customer.honeywell.com/resources/techlit/TechLitDocuments/69-0000s/69-2210EF.pdf
That isn't going to be a good match for what you have. You would be limited to just a single fan speed for one. What was the old thermostat make and part number if you have it?
I will go ahead and opt out of this as I don't have the information on the interchange. Perhaps another tech here might.