Hi Folks,
I have a basic Honneywell programmable electronic thermostat (Honeywell RTH221B) that I would like to use to replace the existing very basic and very old (turn knob type) thermostat in my apartment.
I read the install manual but it doesn't tell me where to connect the existing wiring.
The existing wiring is simple and consists of two thick wires that are connected to the existing thermostat: one red and one black.
The back panel of the new thermostat has 5 options as stated below:

Y -o o- Rh
G -o o- Rc
o- W

I assume that there are only two of these that correspond to the temp switch that I want my existing wires to be on, but which?

And finally, there is a jumper that can be set in either HG or HE position. But I guess that from the manual the jumper has something to with the fan operation (which in my system is systematic every time the 2 wall blow heaters go on.

Thanks for your help,
Dan

Red,if checked with a meter, should be hot,24 volts,it goes to the Rh post,, the black,should go to the W post, you shouldn`t have to worrie about the jumpered wire

I tried what you advised above but this fried my thermostat because I didn't have a meter to check voltage and it was apparently much higher. The wires are enormous. This is most likely the actual power supply of the units themselves which do not have any kind of control mechanism of their own it seems. That's not a very bug deal. These things are only about 20 bucks. But could you please advise on what to do to install a programmable themostat anyway.
Thx
Dan

I am not sure I would have caught the reference to thick wires either. Likely what you have is a line voltage thermostat for an electric heater. Yes, the 120 volts fries regular 24 volt thermostats now and then. With the power on you could carefully touch the wires to the prongs of a lamp plug. It the bulb lights, you have a 120 volt heater and need a line voltage thermostat. If the bulb blows out, make it a 240 volt one. Make sure the thermostat is rated at least as much as the breaker feeding the circuit. If you buy a single pole thermostat, it will only have 2 terminals.

Safest and surest thing is to use a meter. To do simple checks like this you do need some tools. A test light, a meter, or a voltage detector might be the best place to start with. I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. You do not have to open up housings and expose electrical contacts. You are looking at where your hand is, not where the meter is. Most people are capable of doing repairs and will get it going and not get hurt if they use a little sense. The voltage detector makes it even easier.