Our house has its original Gaffers & Sattler furnace (installed in the 1970's). I am replacing the old (original thermostat) with a digital one and have a dilemma. There are four wires strung together coming out of the furnace: Red, White, Blue, and Green. The old thermostat was broken off the wall when some furniture was moved down the hallway, so I don't know which wires were connected. Attached is a picture I found online of a thermostat that looks similar to the old one. The replacement is a Honeywell RTH111. It just needs to heat up and for the fan to work. Any help is appreciated.
Respectfully, Radji

ps: we've already had an HVAC technician out. He couldn't decipher the wiring and would not randomly jump wires to see what happened because the furnace is so old.

I don't know what wires went where on the old thermostat. We were moving a pool table down the hall and it clipped...or really ripped the old thermostat off the wall. I have no idea what wires went where since the old one is broken into about 5 pieces.

Here is a picture of how the wires go into the furnace and of the furnace itself. I can trace them farther than that but I need some instruction on just how to remove the front panel on the furnace in order to trace them. Do I just remove the two bolts at the top or does the side panel need to come off too? Thanks.