Did not label wires from a general control T-90 thermosat Duh! It has a 4 wire line red, blue, white and green. I saw on a earlier post that T-90 has g,f,c,h,v on its sat. The new sat is a honeywell w/ rh, rc,w,y,g. The blue & red wires are hot.

Didn`t see a question,, did you say on a 4 wire system both the red and blue are hot? Go to your furnace take a look-see what is each wire attached

... and what are you trying to control: furnace, heat pump, A/C, boiler, one or more of these, etc.

This is the second time for this question. You need to keep your posts together.

It is a shame you did not write down which color wire went where on the old thermostat. Without that knowledge wiring the new thermostat can be guess work and that is not good. I suggest you go to the furnace and see where the wires for the thermostat are hooked to. List the terminals G,W.Y.R, etc with the color of wire attached to that terminal. Then post that info back here so we can figure it out and be accurate about it so no damage happens to your new thermostat or equipment


Your other post

https://www.askmehelpdesk.com/heating-air-conditioning/change-old-thermosat-new-one-306040.html