I am replacing my old ITT T80BV100J (for use with millivolt, 24 VDC @ 0.60 amp) controlling my existing gas fired gravity floor furnace with a new Honeywell CT50K standard t-stat. Connecting to the new Honeywell seems straightforward with terminals R for power and W for heating. The old ITT t-stat though has no markings on the connectors one on left and the other on the right. Can anyone help me with which one is which on the old t-stat?

I am replacing my old ITT T80BV100J (for use with millivolt, 24 VDC @ 0.60 amp) controlling my existing gas fired gravity floor furnace with a new Honeywell CT50K standard t-stat. Connecting to the new Honeywell seems straightforward with terminals R for power and W for heating. The old ITT t-stat though has no markings on the connectors one on left and the other on the right. Can anyone help me with which one is which on the old t-stat?

First is the new thermostat compatible with a millivolt system? Many are not and it should state weather or not the new thermostat is on the directions or box it came in.

Two wires are two wires not much of a mystery. Pick any one of the two and land it on any thermostat terminal and do the same with the other wire BUT check to be sure the thermostat is compatible as mentioned before you do anything.