I am replacing a honeywell thermostat. I only have 4 wires coming out of my wall.
Green--wired to the 'C' on the old thermostat
Red----wired to the 'C' on the old thermostat
White---wired to the 'W' on the old thermostat
Black---wired to the 'P' on the old thermostat

I purchased a RTH7500 and don't know what I need hook the wires to..

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Originally Posted by acvacvacv3

I am replacing a honeywell thermostat. I only have 4 wires coming out of my wall.
green--wired to the 'C' on the old thermostat
red----wired to the 'C' on the old thermostat
white---wired to the 'W' on the old thermostat
black---wired to the 'P' on the old thermostat

I purchased a RTH7500 and don't know what I need hook the wires to..

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WOW I don't know what kind of thermostat you had but I have never heard of terminals like you quoted. Here is the normal wiring on a four wire thermostat heating and cooling thermostat with out a heat pump.

Red goes to the R terminal. The is the hot wire coming from the transformer.

White goes to the W terminal this the wire that takes the power back to the gas valve.

Green goes to the G terminal This wire takes the power back to the AC blower relay.

The other terminal on the thermostat is Y which takes the power back to the AC contactor.
But since you have a black wire I am assuming that it is the wire that goes on the B terminal. Normally this wire is either yellow or blue.

To test this wire out before you put the thermostat on touch the black wire to the red wire, have someone outside to listen if the condensing unit starts. If it does that pretty well assures that the black wire is the right wire. Of course you can also do this with the white to see if the gas valve opens, If you have a newer furnace you may have a draft assist blower and this will come on before the gas valve opens, so if it does come on then the wire is right. Then the green and red the green to see if the blower comes on. Good Luck

I certainly wouldn't go assuming any of wires follow the conventional color code. If the red was hot from the transformer and the green connected to the blower relay, if they were both connected to the same C terminal, the blower would run continually.

I would go the sticky at the top of the H&AC forum, https://www.askmehelpdesk.com/heatin...ons-58313.html and find the section for your system. There is also a good description of the thermostat wire colors and their function. Before connecting any wires to the new thermostat, make sure where they connect at the heating system. It may have terminals labeled just like the new thermostat.

If you need more help after looking at the sticky, post back.

You could jump it with a jumping cable and see wich is for wich but most likely you are right red to are whit to w green to g black is probably commen back to your transformer (s2)