I need to replace some old mercury bulb heat pump tstats in my home with new digital tstats. The existing tstats are White-Rodgers 1F58-58. The systems work fine, I just want programmability. The heat pump systems are 1 stage cool/2 stage heat systems. I found an installation manual for the existing tstats online. However, when I opened the existing tstats expecting to find 8 wires (terminals R,G,L,C,E,W2,Y, & O) I only found 6 (terminals R,G,C,W2,Y,O). Terminals L & E did not have wires connected to them, nor were there any wires to connect to them. Do I need to pull a new tstat cable with 8 wires for a 7 day programmable tstat (Honeywell)? Or will the 6 existing wires to the job. Why doesn't the emergency heat relay terminal L have a wire? Our HVAC tech has told me that we have emergency heat functionality if the outdoor unit were to fail.

Above your post are 3 stickys that would help you. Try reading this thread completely https://www.askmehelpdesk.com/heatin...eat-58313.html especially post #3

You can use the common for the e , but then you will be changing batteries a lot more often