Have changed a gas furnace old furnace had thermostat wired as followed red to r white to white green to green black to red on outside unit and white from outside unit to white now does it wire back the same on new furnace new furnace is a selg ignt gas unit

I would wire your new unit as called for in the manufactures instructions that come with the furnace. Usually the diagram is located on the inside of the furnace door.

I need to know were to hook wires x b & w2 up on a honeywell rth3100c

Your thermostat may have more terminals than your new furnace needs. There is an extensive discussion of thermostat wires and their colors and functions at https://www.askmehelpdesk.com/heating-air-conditioning/heating-cooling-maintenance-repair-troubleshooting-frequently-asked-questions-58313.html