Furnace not working with thermostat

I have a 2017 Grand Design Reflection 337rls, having problems with furnace not coming on when thermostat calls for it. Ac works great on thermostat, but go to heat nothing. Bench tested and jump out blue wires at furnace and it runs great! Replaced  most furnace parts while I had it out, sail switch, overload switch and circuit board just because it's getting older, test for volts on blue wires coming from ac, o volts there. Furnace is a Dometic SF-35Q, checked wires on roof ac,and inside of ac, all good. So trying to find where the blue wires to furnace are coming from? Control box by ac unit I'm thinking, but no blue wires that size coming off it, also n at the thermostat red wire is 13volts, white wire is 9.7 volts, yellow wire is 13 volts, where do you think my problem is at?