You need to look at your installation instructions. My suburban is really old. Probably almost as old as my 30+ year old RV. So I'm not sure if this will help you. If not let me know and I will find the troubleshooting links for the suburban furnaces that I have booked maked on the computer.
From my furnace. I have two blue wires, a red, a yellow. One of the blue wires comes out of the same connection as the red wire.
The blue wire that comes out with the red wire is connected the lightweight wire (red) which goes to the mechanical thermostat (yellow wire at top left hand side of thermostat in pic). The other blue wire goes to the white wire that runs to the thermostat (ground screw at bottom left hand side of thermostat pic). The red wire goes to the blue RV 12vDC (+) wire and the yellow wire goes to the white RV 12vDC (-)
I have a White-Rodger brand thermostat that is a Heat Only mechanical thermostat (I think I bought the thermostat in GA at Home Depot but not sure). We did replace the older thermostat because it wasn't working right.
Our furnace was working great until we headed down to TX (Nov 2009) I blew a rear outside tire (I have rear duallys on the Class C) that was under the furnace. Got the tire fixed and headed on down the road. Got to TX and the furnace wasn't working. We halfheartedly fiddled with it over that winter but really wasn't that into getting it fixed because the electric heat was cheaper than the propane. Once we got back to NM, we tore into the furnace (pulled it completely out of the RV). I was in need of a good cleaning so we did that. Turned out the flat tire beat the wheel well that the furnace sits on hard enough to beat rust that was inside the tubing loose and the little flecks of rust was blocking the orifice to the burner. The furnace would try to light but it would go right back out. Now it works great again. But we only use it as a back up to the electric heater since our electric is included in our site rental.