One thing to consider
I dont know what kind of furnace you have, but if it is electric, watch out!Your transformer is probably 240volt. Either way it should be located inside furnace. And there usually is a safety switch on the cover like dome light in car, you might have to depress this to test things. Let us know what you find, and how many wires are in t-stat cable, we might need to use these later.. Good luck KOK328 is dead on on test methods, but make sure your not a electric furn. or you'll want to have meter on 240v...
See my work-Check out my album. "Git 'Er Done":D