2 Wire White-Rogers with no wallplate wire question
Hi there.
I want to replace my current White-Rogers 1E56W309 thermostat with a new Honeywell RTH7500D. The problem is that the tools that installed my high efficiency furnace didn't install the wall plate with my thermostat (it was a new house and the builder contracted these guys). Instead, they wired the two wires directly to screws on the thermostat. The dilemma that leaves me is that I have no terminal labels for the current wire placement.
From what I've read, I'm pretty sure that the two wires I have are for terminals R and W. One wire is red and one is black. However, if I look at the wire connections to the current thermostat, the red wire is connected on the left to a screw that has another wire running to the mercury bulb. The black wire is located on a screw to the right and does not have any other wires connected to it via the front of the thermostat.
So my questions are this:
1) Do you agree that the two wires will be R and W?
2) My theory is that the red wire on the screw that has another wire connecting to the mercury bulb is my R wire which, through process of elimination would mean my black wire is my W. Do you agree with my theory?
I don't want to find that I've mixed up my R and W wires while trying to replace a simple 2 wire thermostat. Any confident advice would be greatly appreciated.